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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.
Basin prioritization is a process of classifying the State’s 515 groundwater basins 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) have identified as potential groundwater threats are included on the 6800 Groundwater Protection List. The DPR includes agricultural pesticides on the 6800 list that exceed thresholds values for mobility and persistence and are meant to be applied or injected directly into soil. The DPR is required to monitor for these pesticides in groundwater.
The Affordability Assessment is conducted annually by the California State Water Board to identify community water systems serving disadvantaged communities (DAC) and severely disadvantaged communities (SDAC) with customer charges that exceed the “Affordability Threshold” set by the State Water Board.
Water systems were assigned an affordability burden level as part of the California State Water Board’s Affordability Assessment. Water systems were determined to face a high level of burden if three affordability indicator thresholds were exceeded, medium if two were exceeded, low if one was exceeded, and none if zero thresholds were exceeded.  
The affordability indicators were used by the State Water Board in their Affordability Assessment to determine the overall Affordability Burden faced by water systems. These measurements include Percent Median Household Income, Extreme Water Bill, and Household Socioeconomic burden.  
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.
Animal agriculture operations in this layer include confined livestock areas, dairies, poultry facilities, aquaculture, and facilities with active or historical permits to discharge animal waste. Some of these facilities meet the definition of a Concentrated Animal Feeding Operation (CAFO) and/or Confined Animal Facility (CAF). Public Land Survey System (PLSS) sections with at least one animal agriculture operation are displayed and those with CAFOs are flagged. 
Concentrated Animal Feeding Operations (CAFOs) and other Confined Animal Facilities (CAFs) require permits to discharge waste due to the risk of contaminating surface and groundwater with pathogens and nitrates. CAFOs are regulated under the U.S. EPA’s National Pollution Discharge Elimination System (NPDES) as point source polluters, while other CAFs follow California’s waste discharge standards and are classified as non-point sources.  
An aquifer is the rocky structure underground that holds groundwater. Aquifers are filled when rain and melting snow sinks into the earth. 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. Factsheets: 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). For more information, visit this site.
Biosolids are treated sewage sludge from wastewater treatment plants (WWTPs) that meet regulations for land application as fertilizer or soil amendments. Biosolids are treated to remove pathogens and metals but may contain PFAS due to unregulated contamination in WWTP waste. To learn more, click here. This layer shows approximate locations for sites with current or historical (1995-2024) permits to apply biosolids.
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.
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.
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.
Concentrated Animal Feeding Operations (CAFOs) are industrial-sized Confined Animal Facilities (CAFs) that meet certain criteria for the number of animals and/or method of waste discharge.
Confined Animal Facilities (CAFs), also known as Animal Feeding Operations (AFOs), are defined by the state of California as locations where animals are held and fed by means other than grazing. CAFs include Concentrated Animal Feeding Operations (CAFOs). To learn more, click here.
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.
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).
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.
The California Department of Pesticide Regulation (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 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 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. 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 one square mile Public Land Survey System section. 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 one square mile Public Land Survey System section. 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 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.
The drought analysis indicates potential domestic well impacts in California's Central Valley under Sustainable Groundwater Management Act (SGMA)-related conditions. Wells were predicted to be fully dewatered, partially dewatered, or not impacted if groundwater levels were to reach the depth to Measurable Objectives (MO) and Minimum Thresholds (MT) set by Groundwater Sustainability Agencies (GSAs) in their Groundwater Sustainability Plans (GSPs). More detailed methodology is available here.
Wastewater from treatment plants that flow out into surface waters, either treated or untreated.
Extreme Water Bill is a measure that assesses drinking water customer charges that are at least 150% of the statewide average drinking water charges for six HCF per month. The threshold for this indicator is greater than 150% of the statewide average.
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.
Fully dewatered means the domestic well has gone dry and can no longer draw water. Wells were predicted to be fully dewatered if the perforated interval was located above the Measurable Objectives (MO) and Minimum Thresholds (MT) groundwater level.
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 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. 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. There is no federal maximum contaminant level (MCL) for Cr(VI), but California established an MCL of 10 µg/L. Factsheets: English / Español.
Household Socioeconomic Burden is a composite measure identifying systems serving communities with high poverty and high housing costs for low-income households. The threshold for this indicator is a combined score between 0.25 to 1.00.  
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 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. As PFAS-containing waste materials break down, PFAS may be released into the environment.
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 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.
The Measurable Objective (MO) represents a specific, quantifiable goal for maintaining or improving groundwater level conditions to achieve long-term groundwater basin sustainability and avoid any undesirable results (defined as: significant and unreasonable declines in groundwater levels, reductions in groundwater storage, intrusion of seawater, degradation of water quality, subsidence of land, and depletions of interconnected surface waters).
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 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 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 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.
The Minimum Threshold (MT) represents the groundwater level at which any undesirable results are expected to occur (defined as: significant and unreasonable declines in groundwater levels, reductions in groundwater storage, intrusion of seawater, degradation of water quality, subsidence of land, and depletions of interconnected surface waters).
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.
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 and other harmful organic compounds into well water.
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.
The Organization for Economic Cooperation and Development (OECD) defines PFAS as chemicals with at least one perfluorinated methyl group (−CF3) or a perfluorinated methylene group (−CF2−). 
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 layer displays airports with either current or historical (2014 – 2022) P-139 certification and are considered potential PFAS sources.
Partially dewatered means the surrounding groundwater levels have lowered and reduced the well’s capacity to draw water. Wells were predicted to be partially dewatered if any part of the perforated interval was intersected by the Measurable Objectives (MO) and Minimum Thresholds (MT) groundwater level.
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.
Percent Median Household Income is a measure that compares the average annual residential water bill (for six hundred cubic feet [HCF] per month) to the annual median household income of the service area. The threshold for this indicator is a 1.5% median household income or greater.
The perforated interval of a domestic well refers to the section of the well's casing (the metal pipe that lines the well) containing holes (perforations) that allow groundwater to enter the well.
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 layer shows applications of 166 pesticide active ingredients that pose a threat to groundwater quality. The total pounds of active ingredients applied per square kilometer between 2011 and 2019 are displayed for public land survey system (PLSS) sections.
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 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 MCLs. 
In April 2024, the US Environmental Protection Agency (EPA) finalized six new federal maximum contaminant levels (MCLs) for six PFAS chemicals: 4 ppt for perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA); 10 ppt for perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), and hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX Chemicals); and a hazard index of 1.0 for a mixture of two or more of the following four PFAS: PFNA, HFPO-DA, PFHxS, and perfluorobutane sulfonic acid (PFBS). 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 PFAS Hazard Index is calculated. PFAS regulations are rapidly changing, for up to date information click on the following links: more information on PFAS and EPA MCLs.
This layer shows applications of 48 pesticide active ingredients that meet the Organization for Economic Cooperation and Development (OECD) definition of a PFAS (Donley et al., 2024). The total pounds of active ingredients applied per square kilometer between 2019-2022 is displayed by Public Land Survey System (PLSS) section.
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 (soil, groundwater, etc.).
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).
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 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 2017-2021 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 (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). 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.
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. This is the unit of analysis for the domestic well area layer and the drought scenario analysis.
A severely disadvantaged community (SDAC) is one with an annual 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 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.
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 Drinking Water 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 and is regulated differently than 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.
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.
The California State Water Resources Control Board (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.
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 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.
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) 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.
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).
Start by zooming the map to an area of interest to you. Enter an address or a town/city name.
Select an interactive area to show. You can select an area from the table or by clicking the map to see detailed information, while you have one of these active.
Select any of these layers to see data displayed for water systems and private domestic well communities.
These layers show you four groundwater contaminants for water systems and private domestic wells, with results provided in relation to the regulatory standard (MCL).
This section includes the results of the Central Valley drought scenario analysis for small water system supply wells and private domestic wells. Results are also summarized for counties and GSAs.
Demographic layers here are for three census geometries, and includes the 2017 5-year estimates from the American Community Survey and uses state criteria to identify disadvantaged communities (DACs).
Additional reference boundaries are available here, like DWR B118 groundwater basins.