Arsenic in Drinking Water: What a 20-Year JAMA Study Says About Cutting Exposure

Arsenic has no taste, no smell, and no color. You can't spot it in a glass of water, and neither can your kids. In November 2025, JAMA published a study that followed more than 11,000 adults in Bangladesh for about 20 years. The researchers asked a simple question. Does your health improve if you lower your arsenic exposure? The answer was encouraging, because people whose arsenic levels dropped had far lower death rates from chronic disease, including cancer and heart disease, than people whose exposure stayed high.

What is arsenic, and why is it in drinking water?

Arsenic is a naturally occurring element found in rocks and soil. It dissolves into groundwater, which is why wells in some regions carry high levels without any industrial pollution nearby. The study authors say arsenic in drinking water affects more than 100 million people around the world. In Bangladesh alone, more than 50 million people have been exposed to water above the World Health Organization guideline of 10 micrograms per liter. Earlier research from Argentina, Bangladesh, Chile, Taiwan, and the United States linked long-term arsenic exposure to higher death rates, including from cancer and cardiovascular disease. What nobody knew was how much it helps when you bring exposure back down.

How the study worked

The study is called the Health Effects of Arsenic Longitudinal Study, or HEALS. Researchers enrolled 11,746 adults in Araihazar, Bangladesh between 2000 and 2002, and they tested all 5,966 wells in a 25 square kilometer area. Well water arsenic ranged from under 1 microgram per liter to 864, with an average of 102. Participants gave urine samples up to five times through 2018, which tracked the arsenic actually getting into their bodies. The team followed deaths through 2022, and the final analysis included 10,977 people. Over an average of 19.5 years, 1,401 participants died from chronic diseases, including 256 from cancer and 730 from cardiovascular disease.

How exposure dropped during the study

A mitigation program ran in the same area while the study was underway. Researchers labeled wells with placards that showed whether the water met the Bangladesh standard of 50 micrograms per liter. Health educators told households with high arsenic to switch to safer wells, and the government installed deep, low arsenic community wells in the hardest hit villages. Many families also reinstalled their own wells at greater depths after they saw their test results. Average well water arsenic fell from 102 to 32 micrograms per liter over the study, and average urinary arsenic fell from 283 to 132 micrograms per gram of creatinine. Not every household cut its exposure, and that unplanned gap gave researchers a natural comparison group.

What the researchers found

Lower arsenic meant lower mortality, and the effect grew with the size of the drop. Each decrease of 197 micrograms per gram of creatinine in urinary arsenic was linked to 22 percent lower chronic disease mortality. The same decrease was tied to 20 percent lower cancer mortality and 23 percent lower cardiovascular disease mortality. Larger reductions were linked to steadily lower risk, while increases in arsenic were linked to higher risk. The authors call this a dose response pattern, which means more reduction goes with more benefit. That pattern makes the finding harder to dismiss as a fluke.

People who cut their exposure caught up to the low exposure group

The researchers sorted participants into four groups based on how their urinary arsenic changed. About 45 percent stayed low the whole time, 34 percent went from high to low, 16 percent stayed high, and 5 percent went from low to high. People who dropped from high to low had 54 percent lower chronic disease mortality than people who stayed high. Their cancer mortality was 49 percent lower, and their cardiovascular disease mortality was 57 percent lower. Those results looked similar to the group that was low from the start. People whose arsenic rose had mortality comparable to the group that stayed high, so the direction of change mattered.

What the numbers mean in real terms

The study also estimated how many deaths a bigger reduction could have prevented. If everyone who stayed highly exposed had dropped to low levels, the authors estimate about 5.1 fewer chronic disease deaths per 1,000 person years. They put the share of chronic disease deaths tied to staying highly exposed at 32 percent. The estimates for cancer and cardiovascular disease were 28 percent and 36 percent. These are modeled estimates built on an observational study, so treat them as a sense of scale and not a guarantee. Even so, the size of the gap is hard to ignore.

What this study can't tell you

This was an observational study, so it shows an association and cannot prove that lower arsenic caused the lower death rates. People who cut their exposure tended to have more education and more household assets. The researchers used statistical matching to account for that, and the results held up, but they say unmeasured factors can't be fully ruled out. The study took place in one rural area of Bangladesh, which may limit how well the results apply elsewhere. The team also could not track changes in other metals, and causes of death came from interviews with families, which can contain errors. Good science includes its limits, and these are worth knowing before you draw conclusions.

What this means if you live in the United States

Public water systems in the United States must meet the EPA limit of 10 parts per billion for arsenic. The average exposure in this study was ten times higher than that. So the study does not say your city tap water is causing these outcomes. The authors do conclude that reducing arsenic is linked to better health even at moderate exposure levels, which matters for anyone with a naturally elevated source. Private wells are the biggest concern, because no utility tests them for you and the EPA limit doesn't apply to them. If you rely on a well, you are the only one watching your arsenic level.

How to find out if your water contains arsenic

Test your water with an accredited lab and ask specifically for an arsenic panel. Arsenic levels can differ a lot from one well to the next, even between neighbors. In this study, many families reached safer water simply by drilling deeper, which shows how much the source matters. If you're on a public system, read your utility's annual water quality report and look for the arsenic result. Keep your lab results so you can compare them over time, and retest after any change to your well or your treatment system. A single test only tells you about the day you collected the sample.

How reverse osmosis helps reduce arsenic

Reverse osmosis pushes water through a membrane with extremely small pores that block many dissolved contaminants, including arsenic. Performance depends on the system and on the form of arsenic in your water. Arsenic comes in two main forms, and the membrane removes one form much better than the other unless the water is treated first. So check the product's NSF/ANSI certification and make sure it lists arsenic reduction. If your well test shows high arsenic, talk with a water treatment professional before you pick a system. Then test your filtered water to confirm the system works in your home.

At Sanavia Water, we build reverse osmosis systems for homeowners who live in areas with documented water contamination, including heavy metals, nitrates, and PFAS. We believe you should see the data and make your own call. Our team can help you read a water test and choose a system that fits your home. You don't need a science degree to make a smart decision about your water. You just need good information and a plan.

Frequently asked questions about arsenic in drinking water Does reducing arsenic exposure lower the risk of cancer and heart disease?

In this JAMA study, people whose arsenic levels dropped had lower death rates from both cancer and cardiovascular disease. Participants who went from high to low exposure had about half the chronic disease mortality of those who stayed high. The study is observational, so it shows a strong association and does not prove cause. Still, the pattern was consistent across many different analyses. If you have health concerns, talk with your doctor.

Is there arsenic in US tap water?

Arsenic occurs naturally in groundwater, so some US water sources contain it. Public water systems must meet the EPA limit of 10 parts per billion. Your utility's annual water quality report shows the arsenic level for your system. Private well owners have no utility testing for them, so they need to test their own water. A lab test is the only way to know what's in your glass.

How do I test my well for arsenic?

Use an accredited lab and request an arsenic test, since a basic home test strip won't give you reliable numbers. Your local health department can often point you to certified labs in your area. Test your well on a regular schedule and after any major change to the well. Arsenic can vary from well to well, so your neighbor's result doesn't tell you much about yours. Keep every report so you can spot changes over time.

Does reverse osmosis remove arsenic?

Reverse osmosis can reduce arsenic in drinking water. How well it works depends on the form of arsenic in your water and on the specific system. Look for NSF/ANSI certification that lists arsenic reduction for the product you're considering. If your water has high arsenic, ask a water treatment professional about pretreatment. Always test your water after treatment to confirm the results.

What level of arsenic in water is safe?

The World Health Organization guideline is 10 micrograms per liter, and the EPA limit for public water systems is 10 parts per billion. Those two numbers match, since one microgram per liter equals one part per billion in water. The authors of this study conclude that reducing exposure is linked to better health even at moderate levels. A legal limit is a standard for utilities, and it's not a promise that any amount below it carries zero risk. Many people choose to filter and test for extra confidence.

The bottom line

A 20-year study of more than 11,000 adults found that lowering arsenic exposure was linked to far lower death rates from chronic disease, including cancer and heart disease. People who moved from high to low exposure ended up close to the people who were low all along. The study is observational and took place in rural Bangladesh, so be careful about drawing straight lines to your own home. The practical lesson still applies. Test your water, especially if you use a private well, and treat it with a system backed by real performance data. When you're ready to take the next step, contact Sanavia Water and we'll help you find the right system for your home.

Source: https://jamanetwork.com/journals/jama/fullarticle/2841553?guestAccessKey=31ba480e-32a3-4310-8cf2-7fed9d077681&utm_source=for_the_media&utm_medium=referral&utm_campaign=ftm_links&utm_content=tfl&utm_term=111725#google_vignette