Glossary

1,2,3-Trichloropropane

1,2,3-Trichloropropane (1,2,3-TCP) is a man-made chemical found at industrial and hazardous waste sites. Public water systems statewide have been required to test for 1,2,3-TCP quarterly in their drinking water sources since January 2018. Factsheets: English / Español.

2019 SGMA Basin Prioritization

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.

6800. Groundwater Protection List

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.

Alluvial Boundary

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. 

Aquifer

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

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

Arsenic

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. Factsheets: English / Español.

Asbestos

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.

Basin Plan Management Zones

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). For more information, visit this site.

Biosolids

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

Biosolids

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

Bulletin 118 Groundwater Basin

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 site).

CalEnviroScreen 4.0

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 Facility

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.

Community Water System

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.

Consumer Confidence Report (CCR)

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.

Cost to Remediate Impacted Domestic Wells

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

Cost to Remediate Impacted Public Supply Wells

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).

County

Counties are local administrative units and have defined drinking water and groundwater oversight responsibilities. Counties have existing and new responsibilities under the Sustainable Groundwater Management Act (SGMA).

Critically Overdrafted Basins (2018)

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.

Department of Pesticide Regulation (DPR)

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.

Dioxin

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.

Disadvantaged Community (DAC)

A disadvantaged community (DAC) is one with an annual 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 annual MHI of less than 60% of California’s overall MHI: the calculated SDAC threshold is $50,458 (2021).

Disinfection By-Products

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

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.

Domestic Well

A well on private property that serves no more than four households. The Sustainable Groundwater Management Act (SGMA) is intended to ensure ongoing drinking water access for domestic well users.

Domestic Well Area

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.

Domestic Well Count

This layer shows the count of domestic wells in a one square mile Public Land Survey System section. Visit the Methodology page to learn how the domestic well area layer was constructed.

Domestic Well Depth

This layer shows the average completed depth (feet) for all domestic wells in a one square mile Public Land Survey System section. Visit the Methodology page to learn how the domestic well area layer was constructed.

Domestic Well Population

This layer shows the estimated population of domestic well users in a one square mile Public Land Survey System section. Visit the Methodology page to learn how the domestic well area layer was constructed and how we estimated the domestic well population.

Drought Scenario

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).

Effluent

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

Feature Class

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.

GeoTracker PFAS Map

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

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.

Groundwater Basin

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.

Groundwater Sustainability Agency (GSA)

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 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.

Groundwater Sustainability Plan (GSP)

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 well

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).

GSA Boundary (SGMA)

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.

Heavy Metals

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

Hexavalent Chromium or Chromium (VI) (Cr(VI) is a carcinogen that can be found in many drinking water systems. There is no federal maximum contaminant level (MCL) for Cr(VI), but California established an MCL of 10 µg/L. Factsheets: English / Español.

Human Right to Water

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.

Human Right to Water Portal

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).

Impacted Domestic Well

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.

Impacted Public Supply Wells

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. 

Investigative Orders

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

Landfills are facilities for the disposal of solid waste materials. As PFAS-containing waste materials break down, PFAS may be released into the environment.

Leachate

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

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 Agency (LPA)

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.

Local Small Water Systems (LSWS)

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

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.

Maximum Contaminant Level (MCL)

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).

Maximum Contaminant Level (MCL) Violation

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.

McCall’s Soil Mobility Adsorption Coefficient (Koc)

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)

Median household income (MHI) values in this tool are the estimated 2017-2021 5-Year Average from the American Community Survey of the US Census (ACS) (more info).

Metadata

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

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 Installations Ranges and Training Areas

Military sites are considered sources of PFAS due to their continued use of PFAS-containing fire fighting foam which is commonly used during training exercises and emergency situations.

milligrams (mg) per liter

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.

Nitrate as Nitrogen (N)

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. Factsheets: English / Español.

Non-Transient Non-Community (NTNC)

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 Wells

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 and other harmful organic compounds into well water.

Operable Units (Superfund Sites)

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.

Part 139 Certified Airports

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.

Per- and polyfluoroalkyl substances (PFAS)

Per- and polyfluoroalkyl substances (PFAS) are a large group of man-made chemicals that are commonly used in consumer and industrial products. PFAS are known as “forever chemicals” due to their ability to persist in the environment and accumulate within the human body. Factsheets: English / Español.

Pesticide

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

Pesticide Active Ingredient

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.

Pesticide Groundwater Threats

This layer shows applications of 166 pesticide active ingredients that pose a threat to groundwater quality. The total pounds of active ingredients applied between 2011 and 2019 are displayed within domestic well areas.

Pesticide Use Reporting Program

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

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.

PFAS Detections in Drinking Water Samples

This layer shows the locations where drinking water samples were collected from public supply wells and tested for PFAS in compliance with the State Water Resources Control Board’s Investigative Orders. Points represent locations where water sampling results were collected, where PFAS were detected at any concentration above the limit of detection (LOD) for any PFAS, and samples that exceed one or more of the EPA proposed MCLs.

PFAS National Primary Drinking Water Proposal Hazard Index

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.

PFAS Sources

Facilities that have stored and/or used materials containing per- and polyfluoroalkyl substances (PFAS) are considered PFAS sources because they may release PFAS into the surrounding environment.

Primary Water Source

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 describes where your water comes from and how the water system needs to treat and filter the water before human consumption. 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).

Proposed PFAS Maximum Contaminant Levels (MCLs)

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.

Public and State Small Water Systems

A public water system is a publicly regulated water supplier that serves 15 or more connections or regularly serves 25 or more people daily for at least 60 days out of the year. Small water systems, including state and local small water systems (SSWS and LSWS), do not meet the requirements of a public water system and are regulated differently. SSWSs have between five and fourteen service connections and LSWSs have between two and four connections.

Public Health Goal (PHG)

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.

Public Supply Well

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.

Public Water System

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

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) (more Info).

Radiation

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

Refineries and Bulk Terminals

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). 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.

Safe and Affordable Funding for Equity and Resilience (SAFER) Dashboard

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.

Safe Drinking Water Act (SDWA)

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).

Section (PLSS)

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. 

Severely Disadvantaged Community (SDAC)

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).

Shapefile

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.  

Small Community Water System

A community water system (CWS) is a publicly regulated water supplier that serves at least 25 people for at least 60 days out of the year or has at least 15 service connections (i.e. households). A small community water system is a CWS that serves no more than 3,300 connections or 10,000 people.

Soil Mobility Rating

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.

State Assembly Districts

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

State Senate Districts

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.

State Small Water System

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.

State Small Water System Point Locations

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 and downloaded from their Clearinghouse in October 2022.

Superfund Sites

Superfund sites are locations with high levels of toxic contamination caused by improper management of hazardous materials used in manufacturing facilities, processing plants, landfills, mining sites, and other industrial sites (see EPA Superfund).

Surface water

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

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.

Sustainable Groundwater Management Act (SGMA)

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

Transient Non-Community (TNC)

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.

US Congressional Districts

The boundaries of California’s 52 United States Congressional Districts in the California Water Data tool are based on boundary lines published by the California Redistricting Commission. To find your representative, visit this site.

Volatile Organic Compounds (VOCs)

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

Wastewater Treatment Facilities

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.

Water Board

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.

Well Completion Report (WCR)

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).