Drought is concentrating naturally occurring arsenic and uranium in private wells across Colorado's San Luis Valley, where rural Hispanic communities have little oversight and few affordable options to make their water safe.
A drought in south-central Colorado is doing something more insidious than drying out farmland. It is also concentrating naturally occurring contaminants in the drinking water of people who often have the fewest resources to treat it.
The San Luis Valley sits on a large aquifer system that has long supported farms, towns and private wells. As that aquifer drops, arsenic, uranium, manganese and selenium that occur naturally in the surrounding rock do not disappear with the water. They can become more concentrated in what remains.
According to Inside Climate News, recent research led by Kathy James of the Colorado School of Public Health found that up to one in four private drinking-water wells tested in the San Luis Valley contained elevated levels of heavy metals such as arsenic and uranium.
The conventional framing of climate change tends to be about absence: less snow, less rain, less water. The San Luis Valley shows the inverse problem. Drought is not only removing something. It is concentrating something dangerous that was already there.
What's actually happening underground
The valley is a high-altitude desert that depends on snowmelt from the surrounding mountains to recharge its aquifer. Inside Climate News reported that the aquifer lost an estimated 1.2 million acre-feet of water between 1976 and 2013, more than five times what Denver consumes in a year. The outlet also reported that Colorado's snowpack, which helps recharge aquifers, was at its lowest level since record-keeping began in 1941.
The chemistry matters. Heavy metals like arsenic and uranium are not being added by a factory in this case. They are in the rock and soil. When groundwater is plentiful and moving through the system, those contaminants can remain diluted. When water levels drop, the same geologic contaminants can show up in higher concentrations.
There is another problem as water sinks deeper. James told Inside Climate News that falling aquifer levels can create more anaerobic conditions underground, which can cause more naturally occurring metals to dissolve into the water.
Julie Zahringer, owner and laboratory director of Sangre de Cristo Laboratory in Alamosa, told Inside Climate News that her lab has tested thousands of wells in the San Luis Valley over more than three decades. Her tests have documented contaminant levels rising during dry periods.
About a quarter of the well water samples tested by the lab in southern Colorado exceed the EPA's maximum contaminant level for arsenic, according to the same report. Zahringer told Inside Climate News that the number is going up.
Who pays for it
The federal Safe Drinking Water Act regulates public water systems. It does not regulate private wells. The EPA says private wells are the main source of drinking water for about 15 percent of Americans, leaving roughly 51 million people responsible for monitoring the safety of their own water. Inside Climate News reported that about a third of San Luis Valley residents rely on private wells.
The valley also has one of the highest poverty rates in Colorado and a large native Hispanic population that has lived on the land for generations. That makes the economics of contamination especially harsh.
A reverse osmosis system can remove heavy metals from household water, but it can cost thousands of dollars to install and hundreds more each year to maintain. Inside Climate News reported that the San Luis Valley's hard water can clog filtration systems faster than in softer-water regions, requiring more frequent replacement. The systems can also waste a significant portion of the water that passes through them, which is a major drawback in a place already running short of water.
Many residents have stopped trusting the tap and rely on bottled water instead.
The health stakes are not abstract. Long-term arsenic exposure is linked by the World Health Organization to cancer, cardiovascular disease, diabetes and developmental harm in children. One Colorado-based study found that low-level arsenic exposure in drinking water was associated with increased risk of coronary heart disease.
The contamination does not necessarily stop at the tap. Arsenic and uranium in irrigation water can also accumulate in crops, creating another possible route for exposure through the food supply.
The pattern, not just the place
The San Luis Valley is specific. The pattern it reveals is not.
Across the American West, communities most exposed to climate-driven water risk are often the ones with the least political and financial power. They are rural. They are poorer. They are often non-white. Many rely on private wells, aging municipal systems and irrigation networks that were not built for a future in which drought concentrates naturally occurring metals in groundwater.
This is the same broader environmental-justice dynamic VegOut has documented elsewhere. An earlier piece on North Carolina's Black communities showed how PFAS contamination from textile manufacturing can concentrate downstream from where industrial decisions are made. Different state, different chemistry, similar burden: people with the fewest resources often face the most expensive consequences.
What makes the San Luis Valley case sharper is that there is no single factory to point at. No obvious villain CEO. The arsenic was already in the geology. Drought and overuse are making the exposure harder to ignore.
What technology can and can't fix
There is some movement on filtration. Inside Climate News reported that researchers at Arizona State University are preparing to field-test a new type of filter designed to remove heavy metals from hard water without wasting water. If it works at the promised price point, it could change the economics of well-water treatment for households that currently cannot afford reverse osmosis.
But filtration is downstream of the larger problem. The aquifer is overallocated. Snowpack is shrinking. A better filter can help a household. It does not refill an aquifer that has been losing water for decades.
Anna Vargas, a sixth-generation San Luis Valley resident and project manager with the San Luis Valley Ecosystem Council, framed the trajectory plainly to Inside Climate News: as the years have gone by, there has been less rain and less snowfall, and the heavy metals will become more concentrated.
That is the fear driving the local response.
What happens next
Researchers at the Colorado School of Public Health have built one of the most detailed datasets on heavy metal distribution in private wells in the Western states. More than 800 private well owners were involved in James's study, and community recruiting filled quickly, a sign of how much demand there is for basic information about what people are drinking.
State lawmakers and county commissioners have been briefed, according to Inside Climate News. So far, action has been limited mostly to more testing.
Testing matters. But a test result without an affordable mitigation pathway can become a more precise diagnosis of a problem a household still cannot afford to fix.
The wider question this story raises is uncomfortable. The U.S. has built much of its drinking-water regulatory regime around public systems, while treating private wells as a smaller, more individual responsibility. Climate-driven drought is testing that assumption. As aquifers across the West drop, the 51 million Americans on private wells may find themselves responsible for chemistry that abundant water once helped keep invisible.
Local educators and activists in San Luis, the oldest continuously occupied town in Colorado, have put the issue in simpler terms. Water access is not just an environmental concern. It is a matter of survival for the community.
