But some communities get all their water from contaminated aquifers and can’t afford to treat it properly, which can threaten public health, according to a report by the State Water Resources Control Board.
In California, the state is only just starting to address the primary source of this contaminant in the San Joaquin Valley’s groundwater: the Valley’s 5 million acres of farmland.
The San Joaquin Valley is particularly hard hit by nitrate: 63 percent of the state’s public water systems that report violations of health standards for the contaminant in 2015 were in the Valley.
"Nitrate is the most critical, the most immediate contaminant in the San Joaquin Valley," Harter says.
State regulators are in the second year of a program to help keep agricultural nitrate out of groundwater in the Central Valley.
Other major human sources of groundwater contaminants in the San Joaquin Valley include pesticides that are banned but still linger in the environment.
In 2015, 60 percent of the state’s public water systems reporting health violations for arsenic were in the Valley, and Madera County drinking water has the highest levels of arsenic statewide.
He only found out when he started working as policy director at the Community Water Center, which advocates for safe drinking water in the San Joaquin Valley, and he realized his town was one that had found the contaminant in its drinking water.
Nelson says drinking water advocates estimate a capital funding need of up to a billion dollars, which would need to be addressed in a future water bond.
"We don’t know how air pollution impacts the body differently from water pollution or how multiple effects work out," Capitman says.

FOUNTAIN — U.S. Air Force contractors on Thursday delivered the first of two $400,000 carbon filters designed to strip away two perfluorinated chemicals contaminating city water supply wells.
Fountain ranks among the most-populated sites around the country and in Korea where the granular-activated-carbon filters are being installed as the Air Force investigates perfluorinated chemicals, or PFCs, spreading from bases, including Peterson Air Force Base east of Colorado Springs.
PFCs have been linked to health harm — low birth rates, and kidney and testicular cancers — but public health epidemiological work in Colorado hasn’t been done.
“We’re a public water system making sure we meet the regulations, even the health-advisory level.
Fountain shifted city supplies to surface water sources after contamination was detected last year at levels above the EPA limit of 70 parts per trillion.
But nearly 80,000 people in Fountain, Security and Widefield, as well as other communities south of Colorado Springs, long have relied on groundwater as a primary source of drinking water.
Air Force engineers currently are focused on removing PFOA and PFOS.
When system operators detect a contaminant “breakthrough,” one tank still filters out contaminants while carbon in the first tank is replaced.
Colorado Department of Public Health and Environment officials regard PFOA, PFOS and PFHpA as chemicals of concern but say there’s not enough scientific data on other PFCs, such as PFHxS.
“It will depend on how often we have to use it to meet peak demand.” Water restrictions last summer reduced water use so that surface water sources met most of the demand.

FOUNTAIN — U.S. Air Force contractors on Thursday delivered the first of two $400,000 carbon filters designed to strip away two perfluorinated chemicals contaminating city water supply wells.
Fountain ranks among the most-populated sites around the country and in Korea where the granular-activated-carbon filters are being installed as the Air Force investigates perfluorinated chemicals, or PFCs, spreading from bases, including Peterson Air Force Base east of Colorado Springs.
PFCs have been linked to health harm — low birth rates, and kidney and testicular cancers — but public health epidemiological work in Colorado hasn’t been done.
“We’re a public water system making sure we meet the regulations, even the health-advisory level.
Fountain shifted city supplies to surface water sources after contamination was detected last year at levels above the EPA limit of 70 parts per trillion.
But nearly 80,000 people in Fountain, Security and Widefield, as well as other communities south of Colorado Springs, long have relied on groundwater as a primary source of drinking water.
Air Force engineers currently are focused on removing PFOA and PFOS.
Colorado Department of Public Health and Environment officials regard PFOA, PFOS and PFHpA as chemicals of concern but say there’s not enough scientific data on other PFCs, such as PFHxS.
The effectiveness of carbon filters removing PFCs from contaminated water depends on how frequently the carbon is changed, Colorado School of Mines environmental engineer Chris Higgins said.
“It will depend on how often we have to use it to meet peak demand.” Water restrictions last summer reduced water use so that surface water sources met most of the demand.

Soda Springs holds open house to talk plant contamination cleanup.
SODA SPRINGS, Idaho (KIFI/KIDK) – In Soda Springs the issue of contaminated ground water from plant chemicals is not a new issue.
“We have some selenium in the water underneath our plant that has moved away from the plant," said Roger Gibson, Monsanto’s plant manager.
Multistate Trust is working with the DEQ and the EPA to clean up the contaminant.
Monsanto is doing the same – working with the EPA and DEQ to clean up the selenium from its site.
Progress studies were done every five years.
“The studies have shown that where the city of Soda Springs gets its drinking water from – those sources are safe," Tanner said.
"And the true message that we just want to deliver is for drinking water, just use city drinking water and there is no additional risk exposure based upon the new information that we have found.” When asked if that ground water would have an effect were to be used for watering a garden or get around pets, Tanner said no.
Though there is no risk or threat to the public, Tanner said the DEQ still has a caution for those in Soda Springs.
Pamphlets at the open house recommend not to use ground water or surface water for cooking, drinking or bathing.

GenX is an emerging contaminant that is still being studied for potential health impacts, but it is similar to other chemical compounds which have been linked to cancer.
The attorneys confirmed that they have been contacted by numerous clients in the Wilmington area suffering from medical issues, and expect to file suit soon against Chemours and DuPont.
“Wilmington residents have been calling us, and my mailbox has been full several times a day,” Baron & Budd environmental law attorney John Fiske told WECT.
“There have been so many people calling us, and they’re calling us with ulcerative colitis.
Summy explained that MTBE tainted the drinking water in one neighborhood, and the company ended up settling for $36 million with about 200 residents affected by the contamination.
Attorneys must prove exactly which chemicals people were exposed to, that those chemicals have been shown to cause certain adverse health effects in humans, and then find people who suffered those ailments.
Baron & Budd said they are handling four cases in other parts of the country, including Barstable, Massachusetts, and Escambia, Florida, involving residents who were exposed to C8, a predecessor of GenX that has been linked to cancer.
Summy said Wilmington is the first place his firm is aware of where GenX contamination has been an issue, and that the city could become the “poster child for GenX contamination.” Chemours claims it received a consent order from the EPA to discharge GenX into the Cape Fear River as long as it was produced as a byproduct while making other chemicals.
The CFPUA is studying various water filtration systems that could be installed to remove most of the GenX and other emerging contaminants in our water supply.
Some residents have also expressed anger that CFPUA knew about GenX in the water months before the public was first made aware of the contaminant in an article in the Wilmington StarNews.

Kaukauna water boil advisory could be lifted Wednesday.
Jeff Feldt, general manager of Kaukauna Utilities, told USA TODAY NETWORK-Wisconsin the first of two crucial water samples shows no contamination in the water supply.
A water main broke at Third and Main streets during construction on Monday.
RELATED:4,000 Kaukauna residents under water boil advisory Tuesday’s sample was taken at noon.
If the Tuesday test also shows no contamination, the advisory could be lifted as soon as Wednesday morning.
"We’ll know tomorrow morning (about the water sample test results), then in consultation with the DNR we could lift the ban," Feldt said.
The utility isolated the break and is working to repair it.
While no homes are without water, the broken water main caused pressure in the water distribution system to drop below recommended levels.
Residents who boil water should make sure the liquid maintains a rolling boil for at least one minute before use, according to the advisory.
Jen Zettel: 920-996-7268, or jzettel@postcrescent.com; on Twitter @jenzettel

Residents in Upper Allen Township should boil their water until further notice after E. coli bacteria was found in the water supply this week.
Suez Water announced the boil order Friday and officials said customers in the Center Square Water System were being notified about the problem through phone messages.
Residents in affected areas should not drink the water or use it for food preparation without boiling it first.
E coli bacteria can make people sick and pose additional risks for the young, old and people with weakened immune systems.
A sample collected Tuesday at a water sample station tested positive for E. coli and additional samples collected Thursday showed a "total coliform positive sample."
Tests at residential customer locations "showed no total coliform or E. coli," according to the Suez announcement.
"We are also conducting a thorough investigation to determine the source of the contamination and will implement corrective action," the statement said.
An announcement on the Suez website said bacterial contamination can occur when increased runoff enters the drinking water source.
It can also happen due to a break in the distribution pipes or a failure in the water treatment process.
The Center Square Water System includes the following streets: Atland Drive Bauman Court Beilman Court Brunswick Avenue Buckingham Avenue Cocklin Court Cope Drive, North Cope Drive, South Derbyshire Avenue Emily Drive Fenwick Avenue Fleming Drive Foribunda Lane Glime Drive Granada Lane Grandia Floria Drive Grantham Road Gregor Court Hawthorne Avenue Herman Drive Kower Court Kower Drive Lancelot Avenue Lobach Drive Merrimac Avenue Norfolk Court Paul Circle Rosegarden Blvd., East Rosegarden Blvd., North Rosegarden Blvd., South Rosegarden Blvd., West Sheffield Ave Shoff Court Stumpstown Road West Lisburn Road Wakefield Avenue White Dawn Lane

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Stuart may try to ID, sue whoever polluted drinking-water wells with PFOS and PFOA.
The water contained high levels of dangerous PFOS and PFOA, chemicals once used to make nonstick pans, fire extinguishing foam and water- and stain-resistant fabrics.
The city closed and replaced the wells that were contaminating the water supply to all customers in 2016, and it continues to incur cleanup costs.
At its June 26 meeting, the City Commission will consider an offer by Florida law firm Morgan & Morgan and national law firm Weitz & Luxenberg to determine how the chemicals got into the well water and represent the city in what could be a nationwide lawsuit.
More: Stuart replaced wells after EPA found too much PFOS and PFOA in drinking water Win-win If the lawsuit is successful, the city will get 60 percent of the money awarded and the law firms 40 percent.
"If they lose the case, there’s no cost to the city," Mortell said.
Stuart would be the first to sign up for the lawsuit, Mortell said.
Cleanup costs Equipment to filter the chemicals out of water will cost "upwards of $600,000," said Dave Peters, Stuart’s assistant public works director.
"The city currently meets all water quality regulations," Peters said.
More: How’s the water?

DALLAS–(BUSINESS WIRE)–The national law firm of Baron & Budd announced today it is investigating potential lawsuits related to a recent finding that The Chemours Company may have contaminated the Cape Fear River in Wilmington, North Carolina with GenX, a dangerous industrial chemical. The firm’s investigation will be led by Shareholder Scott Summy, one of the most successful water contamination litigators in the U.S. Summy and the Baron & Budd team have won over $1 billion for clients. The team represents both individuals who have been impacted by water contamination, as well as public water authorities throughout the country. As the leader of Baron & Budd’s environmental practice, Summy has successfully led a number of high-profile lawsuits that have protected the drinking water of millions of Americans. In 1995, Summy met with Wilmington residents whose water was contaminated by a gas additive called MTBE. As a result of those first meetings, Summy filed his first MTBE lawsuit against Conoco on behalf of Wilmington residents. In 1997, the lawsuit was settled after a Wilmington-based jury rendered a multi-million-dollar verdict to cover the costs of medical monitoring. By 2008, Summy won the largest settlement ever against American oil companies for their part in MTBE contamination, on behalf of public water providers – protecting millions of Americans from unsafe drinking water. Summy and the Baron &…