Glossary

1,2,3-Trichloropropane (1,2,3-TCP) is a manmade chemical found at industrial and hazardous waste sites. It has been used as a cleaning and degreasing solvent and in pesticide products. 1,2,3-TCP is suspected to cause cancer in humans based on evidence from animal studies. Human exposure can occur from drinking water containing 1,2,3-TCP or from inhalation of steam from water containing 1,2,3-TCP, such as when showering. The established State Maximum Contaminant Level (MCL) in drinking water is 0.005 µg/L, or 5 parts per trillion. Public water systems statewide have been required to test for 1,2,3-TCP quarterly in their drinking water sources since January 2018. Based upon data collected by the State Water Resources Control Board between 2007 and 2017, 395 public water supply wells (of 5,863 sampled) had detections above the MCL. Download a factsheet for more information (English / Español).

Basin prioritization is a process of classifying the State’s 515 groundwater basins (as identified in Bulletin 118) into one of four categories high-, medium-, low-, or very low-priority For more information, visit this site.

Pesticide active ingredients that the Department of Pesticide Regulation (DPR) has identified as potential groundwater threats are included on the 6800 Groundwater Protection List. The DPR includes agricultural pesticides on the 6800 list that exceed threshold values for mobility and persistence, are meant to be applied or injected directly into the soil using ground-based application equipment or chemigation (where the pesticides are mixed with irrigation water), or it is recommended or required to follow pesticide application with flood or furrow irrigation (within 72 hours of application). The DPR is required to monitor for these pesticides in groundwater.

The alluvial boundary defines the extent of the alluvial deposits in California’s Central Valley including the Sacramento, San Joaquin, and Tulare Lake groundwater basins as defined by California’s Department of Water Resources Bulletin 118 (Faunt 2012).  Alluvial deposits are generally shallow sand and gravel deposits laid down over time in a river channel or floodplain. The name “alluvial” refers to the loose, unlayered nature of the material – often silt, clay, sand, and gravel. The alluvial boundary is the geographic extent of the drought scenario analysis for domestic wells and small community water systems in the Central Valley.

An aquifer is the rocky structure underground that holds groundwater. Aquifers are filled when rain and melting snow sinks into the earth. They provide California with about a third of its freshwater, including drinking water from wells and irrigation for farmlands. Growing demands for water are draining many aquifers because too much water is being pumped out before rain and melting snow can refill them.

Areal apportionment is the process of assigning estimates from a source layer to an overlapping target layer of differing geography.

Arsenic is a naturally occurring element in rock formations that can be released into groundwater. Human activities like industry and agriculture can release arsenic into the environment and cause it to move to new areas and/or become concentrated in water supplies. Exposure to arsenic is associated with cancers of the lung, liver, kidney and skin, and has been linked to diabetes and cardiovascular disease in humans. The current maximum contaminant level for arsenic in California is 10 µg/L.  Download a factsheet for more information (English / Español).

Asbestos is a group of naturally occurring fibrous minerals used in the production of many commercial products during the 20th century. Breathing in asbestos has been linked to numerous adverse health effects. To learn more, review this factsheet.

Through a State Water Board order, management zones are required to provide free well testing to households in their service area to determine if their well has nitrate contamination levels above the legal limit of 10 mg/L (milligrams per liter). If test results return a nitrate level above the legal limit, the management zone must offer free monthly bottled water deliveries. As residents wait for their well test results, they also have access to free water kiosks in their management zone. For more information, visit this site.

Also known as sludge, biosolids are solid organic waste material, formed as a by-product of sewage treatment.

Biosolids are the solid materials that have been separated from the liquid waste during the wastewater treatment process. They are treated chemically and physically to produce a nutrient-rich sludge often used as a fertilizer. To learn more, click here. 

A Bulletin 118 Groundwater Basin is a groundwater basin defined and characterized by the Department of Water Resources’ Bulletin 118, the official publication on the occurrence and nature of groundwater statewide. Bulletin 118 also provides information and recommendations on groundwater management (see Bulletin 118).

CalEnviroscreen 4.0 (CES) is a screening tool used to identify communities that are disproportionately burdened by multiple sources of pollution and possess population characteristics that make them more sensitive to pollution. CES was developed by California’s Office of Environmental Health Hazard Assessment. Review OEHHA’s resources to learn more about CalEnviroScreen 4.0 and its water quality data.

Chrome plating is the process of coating a metal object with a thin, protective layer of chromium to reduce wear and tear. Since the 1950s, PFAS have been used in the chrome-plating industry to act as a mist and fume suppressant. Wastewater from these facilities has been shown to contain high levels of PFAS and other harmful chemicals including volatile organic compounds (VOCs) and heavy metals. See this factsheet for more information on the use of PFAS in the metal-plating industry.

A community water system (CWS) is a public or private water system that distributes drinking water to a specific group of local residents. An entire system can include wells, pipelines, treatment facilities, staff and more to distribute the drinking water. Many community water systems in the San Joaquin Valley rely on shallow groundwater wells that could go dry or become contaminated. For more information: https://bit.ly/3lCjv21.

The Consumer Confidence Report (CCR) is the annual water quality report that community water systems are required to distribute to customers. CCR’s include important information about whether water supplied is at, above or below maximum contaminant levels (MCLs). The CCR for most community water systems in California can be obtained by visiting the Public Drinking Water Watch database or contacting the system directly.

This is the total cost of the mitigation measures for domestic wells, per drought scenario in the Groundwater Supply layers (see Gailey 2020 for more information).

This is the total cost of the mitigation measures for small community water system public supply wells, per drought scenario in the Groundwater Supply layer (see Gailey 2020 for more information).

Counties are local administrative units and have different drinking water and groundwater oversight responsibilities. Counties have existing and new responsibilities under the Sustainable Groundwater Management Act (SGMA). Each county has information about the number of water systems, disadvantaged communities (census places), and groundwater sustainability agencies in the California Water Data Tool. Visit the Data page for more information.

In 2015, the Department of Water Resources evaluated California’s groundwater basins for conditions of critical overdraft, which occurs when groundwater is being over-pumped before it can be replenished. About half of the critically overdrafted basins are located in the San Joaquin Valley. For more information, visit this site.

The California Department of Pesticide Regulation (DPR) is one of six branches of the California Environmental Protection Agency (EPA). The DPR is responsible for protecting human health and the environment through the regulation of pesticide sales and use. They also strive towards implementing reduced-risk pest management practices.

Dioxins are a group of chemicals that are produced during the production of chlorinated organic compounds, including some herbicides. They can also be produced through waste incineration and forest fires. These chemicals take a long time to break down in the environment and accumulate within the food chain. Some dioxins are highly toxic. To learn more, click here.

A disadvantaged community (DAC) is one with an average Median Household Income (MHI) of less than 80% of California’s overall MHI (Public Resources Code). In 2021, the statewide MHI was $84,097: the calculated DAC threshold is $67,278. A severely disadvantaged community (SDAC) is one with an average MHI of less than 60% of California’s overall MHI: the calculated SDAC threshold is $50,458 (2021). 

Disinfection by-products are formed during the chlorination process. When water is disinfected with chlorine, chlorine reacts with organic matter to create disinfection by-products, such as trihalomethanes (THMs). To learn more, click here. 

Dissolved solids are the combination of organic and inorganic matter that has dissolved in water – also referred to commonly as salinity. Common solids found in water include calcium, sodium, chloride, and nitrate. High concentrations of dissolved solids leads to poor water quality and can make it unsafe for drinking, irrigation, and other uses. For more information, click here.

A well on private property that serves no more than four households. Many of these wells have gone dry during droughts, as groundwater levels drop from increased pumping. The Sustainable Groundwater Management Act (SGMA) is intended to ensure ongoing drinking water access for domestic well users.

This layer combines multiple data sources to identify domestic well areas at the Public Land Survey System (PLSS) section level: 1) domestic well locations, 2) block group geography from the 2020 census, 3) block level population estimates from the 2020 census, 3) public and state small water system boundaries, and 4) residential parcels and building footprints.  A domestic well area is defined as a portion of a PLSS section that has at least one domestic well and intersects with a populated census block (2020). Domestic well communities can overlap with areas also served by a public or state small water system. Please consult the complete methodology described in Rempel & Pace et al., 2023.

This layer shows the count of domestic wells in a section. A section is a one-mile square of the National Public Land Survey System (PLSS). This data came from the Department of Water Resources’ Online System for Well Completion Reports (OSWCR) and was processed by the Water Equity Science Shop. Visit the Methodology page to learn how the domestic well area layer was constructed.

This layer shows the average completed depth (feet) for all domestic wells in a section. A section is a one-mile square of the National Public Land Survey System (PLSS). Points representing wells are displayed at the center of PLSS sections. This data originated from the Online System for Well Completion Reports (OSWCR) and underwent additional processing, as described in Rempel & Pace et al., 2023. Visit the Methodology page to learn how the domestic well area layer was constructed.

This layer shows the estimated population of domestic well users in a section. A section is a one-mile square of the National Public Land Survey System (PLSS). This data was developed by members of the Water Equity Science Shop. Visit the Methodology page to learn how the domestic well area layer was constructed and how we estimated the domestic well population.

A drought scenario in this tool is a scenario of groundwater level decline that is based on observations from the 2012 to 2016 drought. Groundwater level decline was based on a scaled version of the 2012 to 2016 drought (drought factors of 0.5, 0.75, and 1.0) for each drought scenario of 50%, 75%, and 100%, respectively. Impacts and costs to remediate impacts were calculated for small community water systems (<10,000 people served) and domestic wells in the Central Valley (See Gailey 2020 for more information).

Wastewater from treatment plants that flow out into surface waters, either treated or untreated.

A feature class is a collection of features that are represented by the same geography (i.e. lines, polygons, points, etc.). They are stored in computer files including geodatabases or shapefiles.

The State Water Resources Control Board (SWRCB)’s GeoTracker PFAS mapping tool displays the sampling locations and analytical results of PFAS measured in drinking water. Data collection by the SWRCB began in 2019 with an order for water systems near airports with fire training areas and municipal solid waste landfills to collect data. The specifics of this program, and its results are available in further detail here. Data from the GeoTracker PFAS map was used to create the PFAS detections in the drinking water threats layer of the Drinking Water Tool.

Groundwater comes from rain and melting snow that collects underground, where it can be pumped out for drinking or irrigation, or to supply water to the environment. For example: when we drink water from a well, we are drinking groundwater.

A specific area of land that sits over at least one aquifer where the groundwater is being used for many purposes, including but not limited to, drinking water, irrigation, and the environment. California has defined 515 groundwater basins and subbasins that are protected under the Sustainable Groundwater Management Act (SGMA) and managed locally.

A Groundwater Sustainability Agency (GSA) is a locally formed group of people responsible for implementing Sustainable Groundwater Management Act (SGMA) rules for each groundwater basin. Each Groundwater Sustainability Agency (GSA) works together to come up with a Groundwater Sustainability Plan (GSP) that will stabilize local groundwater within 20 years by limiting pumping and helping to flow water back into the ground. For more information: https://bit.ly/3Adi1Ut. 

A Groundwater Sustainability Plan (GSP) is a detailed roadmap for how groundwater basins will reach long-term groundwater sustainability. Locally formed groups called Groundwater Sustainability Agencies (GSAs) prepare and submit the Groundwater Sustainability Plans (GSPs) to the California Department of Water Resources (DWR) for approval. The Department of Water Resources (DWR) tracks their performance over time, and will formally evaluate updated plans submitted by Groundwater Sustainability Agencies (GSAs) every five years.

Groundwater wells are a means of accessing water in underground aquifers. There are two main types of groundwater wells: driven and drilled wells.  Driven wells are built by driving a small-diameter pipe into soft earth, such as sand or gravel. A screen is usually attached to the bottom of the pipe to filter out sand and other particles. Driven wells use water sources close to the surface, are cased continuously and shallow (approximately 30 to 50 feet deep). Drilled wells use drilling equipment and can be drilled more than 1,000 feet deep.  Most modern wells are drilled, which requires a fairly complicated and expensive drill rig. In both types, a pump is often placed in the well at some depth to push the water up to the surface. Community water system supply wells (public supply wells) tend to be deeper than household wells (domestic wells) (Learn More).

The boundary of a Groundwater Sustainability Agency (GSA) is formed in compliance with the State Groundwater Management Act (SGMA).  Data in this tool is based on the Exclusive GSA boundaries available from the Department of Water Resources.

In general, heavy metals are metals with a high density. Examples include gold, silver, tin, copper, zinc, and iron. Although some of these metals, like zinc and iron, are beneficial for health at low doses, others like lead and mercury, can be toxic. 

Hexavalent Chromium or Chromium (VI) (Cr(VI) is a carcinogen that can be found in many drinking water systems. Exposure through skin contact, drinking, eating, or inhaling is associated with cancer, and liver and kidney damage. Animal studies show that drinking water containing Cr(VI) can cause cancers of the mouth and intestines. There is no federal maximum contaminant level (MCL) for Cr(VI), but California is in the process of establishing an MCL of 10 µg/L. In the interim, total chromium (which includes Cr(VI) and other forms of chromium) is regulated in California at 50 µg/L. Download a factsheet for more information (English / Español).

Everyone has a right to safe, clean, accessible, and affordable water. The Human Right to Water is protected by law in California and prioritizes water for personal and domestic uses, such as drinking, cooking and basic hygiene, over industry and agricultural uses. State agencies such as the Department of Water Resources (DWR) and the State Water Resources Control Board (SWRCB) must consider the Human Right to Water when revising, adopting or establishing policies and regulations. For more information: https://bit.ly/3bvdJxc.

The Human Right to Water (HR2W) Portal was launched after California statutorily recognized that “every human being has the right to safe, clean, affordable, and accessible water adequate for human consumption, cooking, and sanitary purposes.” The HR2W Portal provides information and data about progress toward this goal and serves as the state’s primary location for information on water system performance measures, like compliance with the Safe Drinking Water Act (HR2W Portal).

An impacted domestic well is one with at least one of four impacts per drought scenario. The impacts considered are: increased pumping lift, pump cavitation, well screen clogging and wells running dry.

An impacted small community water system public supply well is one with at least one of four impacts per drought scenario. The impacts considered are: increased pumping lift, pump cavitation, well screen clogging and wells running dry. 

The State Water Resources Control Board (SWRCB) identifies and issues investigative orders to facilities that have stored and/or used materials containing per- and polyfluoroalkyl substances (PFAS). Facilities are required to perform a one-time sampling effort to determine PFAS contamination of the surrounding soil, groundwater, surface water, and influent and effluent wastewater. 

Landfills are facilities for the disposal of solid waste materials. Landfills are the final destination for many PFAS-containing products – like furniture, textiles, and carpeting – that have reached the end of their life cycle. As these products break down, PFAS may be released into the environment through landfill discharge (leachate), surface runoff, and evaporation. For more information on PFAS and landfills, read this article. Landfills may also release other harmful organic compounds, volatile organic compounds (VOCs), heavy metals, pharmaceuticals, and personal-care products.

Leachate forms when rain water trickles through a landfill, mixes with the waste materials and draws out some of the chemicals and other components. 

Limit of detection (LOD) is the lowest concentration of the substance being identified that can be reliably measured.  LOD refers to the detectable limit at which water quality contaminants can be reliably measured.

Local Primacy Agencies (LPAs) are responsible for regulating all Public Water Systems (PWSs) within their jurisdiction that have less than 200 service connections. In California, the State Water Resources Control Board (SWRCB) has granted 30 of the 58 county environmental health departments the authority to act as LPAs.

A local small water system (LSWS) is a water system that does not meet the requirements of a public water system. It only serves drinking water to 2-4 connections. The water quality of a LSWS is regulated differently than that of a public water system.

Lowering groundwater levels are defined as the lowering of the elevation of the groundwater table across a whole basin or locally. Groundwater elevation data is available from the Department of Water Resources and is measured as feet above or below mean sea level.

The maximum contaminant level (MCL) is the highest level of a contaminant allowed in drinking water set and enforced by the federal Environmental Protection Agency and the State Water Board. The MCL is set based on the best available treatment technology and cost considerations, therefore, the public health goal (PHG) may be lower than the formal regulatory and enforceable MCL standards (EPA 2019).

A maximum contaminant level (MCL) violation is issued when water from a community water system violates a Safe Drinking Water Act drinking water quality standard.

The soil adsorption coefficient measures the mobility of a substance in soil. High values correspond to less mobile substances while low values correspond to more mobile substances. For more information on the Koc, click here.

Median household income (MHI) values in this tool are the estimated 5-Year Average from the American Community Survey of the US Census (ACS). The Demographic layers (Census Tract, Block Group and Place) and the Public and State Small Water System interactive layer feature the period 2017-2021 5-year estimated MHI (more info).

Metadata contains information about another dataset, including details such as the data source(s), author(s) of the dataset, and methodology used. 

Micrograms (µg) per liter is a standard measurement used to measure how many micrograms of a contaminant are present in one liter of water: 1 µg is 0.001 milligrams.

Military sites are considered to be sources of PFAS due to their continued use of PFAS-containing firefighting foam which is commonly used during training exercises and emergency situations. Military sites also release other kinds of contamination, including heavy metals and radiation.

Milligrams (mg) per liter is a standard measurement used to measure how many milligrams of a contaminant are present in one liter of water: one mg/L is equal to one-millionth of a liter, or one-part per million (ppm), and 1 mg is 1000 micrograms.

Nitrates are chemical compounds made up of nitrogen and oxygen. Nitrates are one of the most common kinds of groundwater contamination. Many fertilizers contain nitrogen and excess nitrate that can enter groundwater through runoff from agricultural areas, gardens, and lawns. Additional sources include animal and human waste and can enter groundwater from dairies, septic tanks, and sewer systems. In the short term, drinking water with unsafe levels of nitrate can cause methemoglobinemia (also known as blue baby syndrome). Infants are particularly vulnerable to methemoglobinemia, which can be fatal without immediate treatment. Other possible health effects of drinking water with high levels of nitrate include pregnancy complications; kidney, spleen, and thyroid damage; and increased cancer risk. If there are high levels of nitrates in your drinking water, boiling, softening, and filtering will not reduce or remove nitrate, and may actually lead to higher concentrations. The current maximum contaminant level (MCL) for nitrate in California is 10 mg/L. Download a factsheet for more information (English / Español).

A non-transient non-community (NTNC) water system serves drinking water to at least the same 25 persons over 6 months per year, but does not meet the requirements of a community water system. These can include businesses, schools, large airports, factories, and hospitals.

Oil and gas activities may lead to groundwater contamination through various pathways including surface spills, fracking, improper management or disposal of wastewater, and deteriorating or improper construction of wells. These conditions can result in the release of PFAS, other harmful organic compounds, volatile organic compounds (VOCs), and dissolved solids into well water. Research has shown that residents living in close proximity to oil and gas wells are more likely to experience adverse health effects such as birth defects, cardiovascular disease, impaired lung function, anxiety and depression (Gonzales, 2023).

During cleanup of a Superfund site, the area can be divided into a number of distinct sections (“units”) depending on the complexity of the problems associated with the site. Operable units may address geographic areas of a site, specific site problems, or areas where a specific action is required.

Public airports in California that are permitted to use aqueous film-forming foam (AFFF) containing PFAS must have a Part 139 certification (P-139) issued by the Federal Aviation Agency (FAA). This tool has information on 36 airports with either current or historical (2014 – 2022) P-139 certification and are considered potential PFAS sources. Other contaminants released by airports include volatile organic compounds (VOCs) and petroleum hydrocarbons.

Per- and polyfluoroalkyl substances (PFAS) are a large group of man-made chemicals that are commonly used in the manufacturing of products to increase resistivity to heat, water, and oil. PFAS are known as “forever chemicals” due to their ability to persist in the environment and accumulate within the human body. PFAS contamination of soil, air, and water can originate from a variety of sources. Exposure to PFAS has been linked to toxic effects including birth defects, cancer, liver disease, and damage to the immune system and thyroid. Even exposure to relatively low doses of PFAS can lead to adverse health outcomes. Download a factsheet for more information (English / Español).

A pesticide is a substance that is used to kill insects, plants, fungi, and other organisms that are harmful to crops or animals.

A pesticide active ingredient is the compound in a pesticide mixture that is responsible for enabling the product to have a desired effect, which can include preventing, destroying, repelling, or mitigating a pest, regulating plants, etc.

This tool displays applications of pesticide active ingredients that were identified as groundwater threats if they met at least one of the following conditions: 1) already being regulated by the Department of Pesticide Regulation as a potential groundwater threat; 2) has a high soil mobility rating; 3) has already been detected in groundwater. Pesticides that met at least one of the aforementioned criteria were considered likely to infiltrate and contaminate groundwater sources. The classes of pesticides most commonly detected in groundwater include organophosphates, organochlorines, and triazines. Exposures to pesticides in drinking water can have varied adverse health effects which depend on the type of chemical, its concentration, and duration of exposure. Repeated exposures to low levels of pesticides commonly found in drinking water can result in birth defects, damage to the nervous system, and cancer. 

The Pesticide Use Reporting (PUR) Program is run by the Department of Pesticide Regulation (DPR). Beginning in 1990, the PUR Program has required that all agricultural and some non-agricultural applications of pesticides be reported on a monthly basis to county agricultural commissioners. Agricultural pesticide use is reported in pounds of active ingredient applied per square mile (Public Land Survey System [PLSS] section). Only legal, agricultural pesticide use is represented in this tool.

Petroleum hydrocarbons are compounds that contain hydrogen and carbon. They are extracted from layers of rock within the earth’s crust and refined to produce fuel.

This layer shows the locations where PFAS were measured or detected in drinking water wells that supply public water systems. The State Water Resources Control Board’s (SWRCB) data collection began in 2019 with an order for water systems near airports with fire training areas and municipal solid waste landfills to collect data. This shapefile represents locations where water sampling results were collected, where PFAS were detected at any concentration above the limit of detection (LOD) for any PFAS, and a subset of samples that exceed one or more of the EPA proposed MCLs. 

The EPA has proposed regulating one or more of 4 PFAS chemicals in a mixture – perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX Chemicals), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS) – using a Hazard Index MCL of 1.0. Hazard indices are useful for understanding health risks associated with exposure to chemical mixtures by accounting for the relative toxicities of each chemical. Click the link to learn how the proposed PFAS Hazard Index is calculated.

Facilities that have stored and/or used materials containing per- and polyfluoroalkyl substances (PFAS) include P-139 airports (i.e. airports certified to use fire fighting foam that contains PFAS), military sites, some superfund sites, chrome-plating facilities, wastewater treatment facilities, landfills, and refineries and bulk terminals. These sites are considered PFAS sources because they may release PFAS into the surrounding environment.

Community water systems are classified based on the presence of certain source types (i.e. any surface water, or any groundwater influenced by surface water).  The primary water source of a community water system indicates the presence of a source type that determines the treatment and filtration requirements for that system. Because surface water and groundwater are treated differently, the primary water source type classification by state and federal agencies allows for higher monitoring and fulfills greater public health protection requirements. 

State and federal drinking water system databases define six categories of primary water sources: 1. groundwater under the direct influence of surface water; 2. purchased groundwater under the direct influence of surface water; 3. groundwater; 4. purchased groundwater; 5. surface water; and 6. purchased surface water (view full definition).

Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are PFAS chemicals that are no longer manufactured or imported into the United States. Exposure to PFOS and PFOA has been linked to adverse effects on fetal development, cancer, liver disease, immune effects, and thyroid effects. In March 2023, the US Environmental Protection Agency (EPA) proposed a federal maximum contaminant level (MCL) of 4 ppt for PFOA and PFOS. The EPA also proposed a Hazard Index MCL of 1.0 to regulate 4 other PFAS chemicals, including perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX Chemicals), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS). PFAS regulations are rapidly changing; for up-to-date information click on the following links: more information on PFAS and proposed MCLs.

A public water system (PWS) is a publicly regulated water supplier that serves 15 or more connections (i.e., households) or regularly serves 25 or more people daily for at least 60 days out of the year. It can be operated or managed by a city, county, water district, investor-owned utility, mobile home park, etc. PWSs include community water systems and other system classifications. For example, a PWS could serve households with year-round residents as well as restaurants, schools, hospitals, campgrounds, or gas stations. 

State small water systems (SSWSs) are water systems that have between 5 – 14 service connections and do not meet the requirements of a public water system. Although they provide piped drinking water, they do not regularly serve drinking water to 15 or more connections (i.e. households) or regularly serve 25 or more people daily for at least 60 days out of the year. The water quality of a SSWS is regulated differently than a public water system.

This tool has information about 4,035 active public and state small water systems (as of 2023), as described in Data. Information on local small water systems (LSWSs), which serve between 2 – 4 connections, is only available for Monterey County. 

Public Health Goals (PHGs) are concentrations of contaminants in drinking water considered safe if ingested at that level continuously throughout life. PHGs are developed and published by the Office of Environmental Health Hazard Assessment (OEHHA) and are based solely on protecting public health. They do not take into account cost or the technology available to achieve that standard (OEHHA 2019). They are only goals and are not enforceable.

A public supply well is a well that serves a public water system. Public supply well location data is available at the section level. A section is a one-mile squared unit of the National Public Land Survey System (PLSS).

A public water system (PWS) is a publicly regulated water supplier that serves 15 or more connections (i.e. households) or regularly serves 25 or more people daily for at least 60 days out of the year. It includes community water systems and other system classifications. For example, a PWS could serve households with year-round residents as well as restaurants, schools, hospitals, campgrounds, or gas stations (SWRCB 2019).

Race and ethnicity data in this tool are from the American Community Survey (ACS) of the US Census 5-Year Average. Each category is shown as a percent of the total population for each census geography (county, place, tract, block group) by eight different race/ethnicity categories. The interactive county layer, the census geographies in the demographic layers, and the public and state small water systems layer feature the 2017-2021 ACS 5-year estimated percentages (More Info).

Radiation is energy that travels from a source in the form of waves or particles. Radiation can occur naturally and is found in soil, water, air and in the body. Depending on many factors, excessive exposure to certain types of radiation can cause damage to human health. Click here to learn more about radiation and health. For information on radiation in drinking water, click here. 

Petroleum refineries are facilities for processing crude oil into petroleum products. Bulk fuel terminals are facilities for the storage of petroleum products (able to store up to 50,000 barrels). The use of PFAS in the operations of bulk fuel storage terminals and refineries is varied. PFAS is used in fire-fighting foam for fire suppression, fire training, and flammable vapor suppression. PFAS is also used in bulk fuel storage tanks as a protective floating layer on the surface to reduce evaporation loss. Read this article for more information on PFAS in refineries and bulk terminals. Refineries and terminals may also release other harmful organic compounds and volatile organic compounds (VOCs).

The Safe and Affordable Funding for Equity and Resilience (SAFER) Dashboard was released in 2022 by the State Water Resources Control Board (Water Board). The dashboard displays a current list of Failing water systems, which is updated daily and based upon criteria set by the Water Board. The dashboard also displays At-Risk water system status, which is updated quarterly and based upon various water system performance metrics, including water quality, accessibility, affordability, and TMF (technical, managerial, and financial) capacity. Data from this dashboard comes from the Water Board, the Department of Water Resources, and the Office of Environmental Health Hazard Assessment. Information from the dashboard is used in the Water Board’s annual Drinking Water Needs Assessment. Click here to access the SAFER Dashboard User Guide.

The Safe Drinking Water Act (SDWA) refers to federal and state laws that provide oversight for the drinking water quality of all water systems in the United States. It is enforced by the federal Environmental Protection Agency (EPA), which sets standards for drinking water quality and implement various technical and financial programs to ensure drinking water safety. In California, the SDWA enforcement authority is delegated to the State Water Resources Control Board by the federal EPA (EPA 2019).

The Public Land Survey System (PLSS) is one way to subdivide and describe public land in the United States. Public land is divided into 6×6 mile units called townships, which are subdivided into 36 1×1 mile grid squares, called sections. In the California Water Data Tool, domestic and public supply well locations are typically located at the center (or centroid) of each 1×1 mile section. This is the unit of analysis for the domestic well areas layer and the drought scenario analysis. 

A severely disadvantaged community (SDAC) is one with an average median household income (MHI) of less than 60% of California’s overall MHI. In 2021, the statewide MHI was $84,097, therefore, the calculated SDAC threshold is $50,458 (Public Resources Code).

A shapefile is a type of computer file that stores information about shapes (lines, points, or areas) on a map. Information about the shapes can include location, sizes, names, etc.  

A community water system (CWS) is a publicly regulated water supplier that serves at least 25 people year-round or has at least 15 service connections (i.e. households). A small community water system is a CWS that serves 10,000 people or fewer.

A soil mobility rating indicates the likelihood of a pesticide moving through the soil and infiltrating groundwater. The Soil Mobility Rating can be determined using McCall’s Soil Mobility Adsorption Coefficient (Koc). A Koc of 150 or below indicates a high likelihood of movement through soil to contaminate groundwater.

The boundaries of California’s 80 state assembly districts in the California Water Data tool are based on boundary lines published by the California Redistricting Commission. To find your assembly member, visit this site.

The boundaries of California’s 40 state senate districts in the California Water Data tool are based on boundary lines published by the California Redistricting Commission. To find your senator, visit this site.

A state small water system (SSWS) is a water system that does not meet the requirements of a public water system. Although they provide piped drinking water, they do not regularly serve drinking water to 15 or more connections (i.e. households) or regularly serve 25 or more people daily for at least 60 days out of the year. The water quality of a SSWS is regulated differently than that of a public water system.

This State Small Water System Location layer displays the point locations for 1,329 state small water systems (SSWS) in California. SSWS serve 5-14 service connections. This dataset was developed by the California State Water Board as an intermediate step toward compliance with Senate Bill 200 (SB 200). Data was downloaded from the California State Water Board Clearinghouse in October 2022. 

Superfund sites are locations with high levels of toxic contamination, including PFAS, heavy metals, asbestos, dioxin, and radiation. Contamination is caused by improper management of hazardous materials used in manufacturing facilities, processing plants, landfills, mining sites, and other industrial sites. The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) was passed in 1980 and gives the EPA the authority to identify and clean up Superfund sites. When applicable, CERCLA requires responsible parties to perform or fund the cleanup efforts themselves. Click the link to learn more about the Superfund program.

Surface water is any body of water above ground, including streams, rivers, lakes, wetlands, reservoirs, and creeks. Surface water is used for many purposes, including drinking and agricultural use, and can be restocked faster than groundwater, depending on the weather. As drought worsens, California has less melting snow to feed rivers in the spring and summer, so less water makes it downstream to reservoirs and canals, which leads to increases in groundwater pumping to meet water demands.

Sustainability means meeting current needs without compromising the needs of future generations. For example, current overpumping of groundwater in the San Joaquin Valley for short term profits is causing land to sink and wells to go dry, and is therefore not sustainable.

The Sustainable Groundwater Management Act (SGMA) is a California law intended to prevent too much water from being pumped out of underground water reserves. Before the Sustainable Groundwater Management Act (SGMA), there were no limits on groundwater use, and cities and farms have been pumping more as drought reduces the amount of water available from rivers and reservoirs. As a result, groundwater levels have dropped across the state. The law was designed to ensure ongoing access to groundwater for drinking, farming, and the environment. For more information: https://bit.ly/3Nrh2Tr. 

A transient non-community (TNC) water system serves drinking water to at least 25 individuals daily (same or different people) at least 60 days out of the year, but does not meet the requirements of a community or non-transient non-community water system. These can include small businesses with less than 25 employees, restaurants, parks, and campgrounds.

United States Congressional Districts. Updated 2022.

Volatile organic compounds (VOCs) are organic compounds (compounds that contain carbon) that are released into the surrounding air at room temperature. Exposure to some VOCs may cause adverse health effects, depending on the level of exposure. For more information, review this factsheet. 

A sewage treatment plant that is owned or operated by a government agency. Wastewater treatment facilities receive wastewater contaminated with PFAS and other chemicals from residential, commercial, and industrial sources. After treatment, the remaining waste – or effluent – is released into the environment, oftentimes still containing high levels of PFAS. Additionally, PFAS may contaminate biosolids which may then be applied to agricultural fields as fertilizer. See this website for more information on PFAS in wastewater treatment facilities. Other chemicals of concern from wastewater treatment facilities include other organic compounds, volatile organic compounds (VOCs), inorganic compounds, disinfection by-products, pharmaceuticals, and personal-care products.

The California State Water Resources Control Board (Water Board) is one of six branches of the California Environmental Protection Agency (EPA). The State Water Board oversees the allocation and use of the state’s water resources to various entities for agricultural irrigation, hydroelectric power generation, and municipal water supplies. It also enforces the Safe Drinking Water Act for public water systems.

When a well is constructed, altered, or destroyed, a well completion report (WCR) is filed with the Department of Water Resources within 60 days of the completion of the work. Well drillers can submit WCRs with the Online System of Well Completion Reports (OSWCR). This OSWCR database is a foundational dataset for several layers in California Water Data Tool. The OSWCR contains both digitized completion reports from historical, paper records and more recently submitted online reports (More info).