With surface water supplies decimated from the ongoing drought, more Californians are forced to use groundwater.
But groundwater is unsafe for nearly 800,000 residents, according to the state's water resources control board.
This problem is the longtime contamination from nitrates and arsenic.
That's meant less drinkable water in California's struggle to survive more than three years of severely dry weather.
"Most areas affected by contamination don't have surface water supplies so they have to find new groundwater sources," said Kurt Souza, a branch chief of the division of drinking water at the California State Water Resources Control Board.
"But that's not always easy to do," Souza added. "Sometimes you can find new ground locations for water and sometimes you can't."
The lack of rain and subsequent heavy demand on ground wells—which are also facing supply problems—is making a bad situation worse, said Sara Aminzadeh, executive director of the California Coastkeeper Alliance, a statewide advocacy group for safe water.
"Contamination is a major concern," Aminzadeh said. "The drought just exacerbates water issues, and the groundwater problem is one of those."
According to the state water resources study, unsafe levels of arsenic are the top contaminant in groundwater supplies, followed by nitrates.
Nitrates are most often traced to farming chemicals and animal waste. Arsenic is found naturally in soil and rock in much of the world and seeps into groundwater.
Chronic low exposure to arsenic has been traced to respiratory problems in children and adults as well as having links to diabetes, cardiovascular diseases and cancers of the skin.
"Arsenic is a known carcinogen and with increased reliance on groundwater in California, the risk of arsenic increases," said Chris Williams, a hydrologist and terrestrial ecosystem ecologist at Clark University.
California seems particularly vulnerable to arsenic contamination, said Francie Cuffney, head of the biological science department at Meredith College.
"It has areas of high arsenic concentration. Groundwater in contact with rocks of high arsenic concentration will naturally leach out arsenic," Cuffney added.
The state water resources board said 98 percent of the 38 million Californians get safe drinking water from public sources and treated groundwater supplies.
But 772,883 Californians rely on groundwater that is contaminated due to the high cost of water treatment or a lack of alternative water sources, according to the board.
Of that number, 400,000 are in the San Joaquin Valley—often referred to as the "food basket of the world" for its agricultural production.
One of the areas hardest hit by contaminants in the valley is Tulare County, where supplies of water bottles at state expense have been dispersed to many residents on a weekly basis, according to county water commission analyst Denise Akins. The county has also provided a 5,000-gallon, non-potable water tank for bathing and flushing.
This is due to hundreds of ground wells drying up from lack of rain—but also because the safety of many has been compromised.
"We have had contamination of arsenic and nitrates," Akins said. "We've delivered water to people that meet the income qualifications and who are in contaminated water areas. But the money to buy the water won't last forever."
Akins explained that the county water commission is planning to find new groundwater wells but is more likely to pay, with state and federal funds, to bring in water from other sources.
"We've talked to a couple of suppliers to set up tanks for people on a regular basis," she said. "We're hoping to have something in place by the end of the year."
In 2012, Gov. Jerry Brown signed legislation establishing a state policy that every Californian has a human right to safe, clean, affordable and accessible drinking water.
A year earlier, he signed seven bills into law seek to improve access to clean drinking water in California.
But experts say there aren't enough enforcement mechanisms in place.
"Many of the groundwater sources in California are not well monitored," said Clark University's Williams. "They need to prioritize that going forward."
With officials admitting something needs to be done, the state water resources control board is updating the 1993 safe drinking water plan and seeking input from the public.
Among the dozens of proposals in draft form are calls for increased funding for research and demonstration grants to develop new treatment processes or improve the cost efficiency of existing treatment processes for small water systems.
But final plans are months away. A quicker resolution might come from state voters in November.
They have a chance to approve a $7.545 billion bond measure.
It targets funding for new surface and groundwater storage projects, as well as for sustainable groundwater management while providing safe drinking water, particularly for disadvantaged communities.
Polls show the measure passing by a wide margin.
But what would help even more are near endless days of rain.
"If we have another dry year, I don't know what we'll do," Akins said. "I don't even want to think about it."