Pharmaceuticals in Tap Water: What USGS Found and What It Means

Yes, trace amounts of pharmaceuticals are found in some US drinking water, mostly at levels measured in nanograms per liter (parts per trillion). US Geological Survey and EPA scientists have detected drugs like carbamazepine, an anti-seizure medicine, in treated tap water. The World Health Organization has concluded that these trace levels are very unlikely to pose a risk to human health because they are far below the doses that have any effect on the body. Long-term exposure to low-level mixtures is still being studied, and in 2026 EPA put pharmaceuticals on its draft list of contaminants it may regulate.

Here’s what the research actually measured, how drugs get into water, what treatment removes, and what you can do if you want to reduce exposure further.

How drugs end up in water

USGS describes three main routes:

People. Many medicines aren’t fully absorbed by the body and pass into toilets. Unused medicine flushed down the drain adds more. Wastewater treatment plants weren’t designed to remove these compounds, and some pass through.
Manufacturing. USGS found that two wastewater plants receiving discharge from drug factories had concentrations 10 to 1,000 times higher than 24 plants without that discharge, with traces detected up to 30 kilometers downstream.
Livestock. Streams near animal feeding operations contained compounds such as acetaminophen, caffeine and carbamazepine.

When treated wastewater flows into a river or lake that another community uses as its water source, some of those traces can reach a drinking water plant.

What USGS found in rivers and streams

The first national look came from a USGS study of 139 streams in 30 states sampled in 1999 and 2000. It tested for 95 “organic wastewater contaminants,” a group that includes pharmaceuticals, hormones, insect repellent, caffeine and household chemicals.

At least one compound was detected in 80% of the streams. Half contained seven or more. USGS noted that concentrations were generally low and rarely exceeded drinking water guidelines, though many of the compounds had no guidelines at all.

Two caveats: the streams were chosen because they were likely to be affected by farms or cities, so the 80% figure isn’t a national average. And these were streams, not tap water.

What was found in source water and treated tap water

The most direct evidence comes from a joint USGS–EPA study of 25 drinking water treatment plants, published in 2017 in Science of the Total Environment. The plants were chosen because their source water was likely to receive wastewater, so they represent a higher-exposure scenario.

What the researchers found:

In the second phase, which tested for 118 pharmaceuticals, 47 were detected in source water. For the drugs they could measure, median source water concentrations were below 113 ng/L.
Far fewer showed up after treatment. The study reports 26 pharmaceuticals detected in treated water in that phase, with a median of two per plant.
Most treated water levels were low. Excluding lithium, the highest Phase II treated water value was 92 ng/L. The highest overall was carbamazepine at 586 ng/L at one plant using a groundwater source that the authors suspected was affected by septic waste.
The compounds that most consistently made it through treatment included carbamazepine, bupropion (an antidepressant), metoprolol (a blood pressure drug), cotinine (a nicotine breakdown product) and lithium.

For scale, 100 ng/L is 100 parts per trillion. Drinking 2 liters of water a day at that level would add up to 0.0002 milligrams of a drug per day. Typical medication doses are measured in milligrams.

Groundwater: fewer detections

Groundwater tends to be better protected. A national USGS study published in 2019 sampled nearly 1,100 wells that tap aquifers supplying about 60% of the groundwater Americans drink. It tested for 103 pharmaceuticals and 21 hormones before any treatment.

About 6% of public-supply wells and 11% of domestic and other wells had one or more of these compounds. USGS said the levels were not expected to have adverse human health effects. Only one sample, containing hydrocortisone, exceeded its human health benchmark. For more on how the two kinds of sources compare, see groundwater vs. surface water quality.

What WHO and EPA say about the risk

WHO. The World Health Organization’s 2012 report Pharmaceuticals in Drinking-water reviewed the research and concluded that trace quantities in drinking water are very unlikely to pose risks to human health. The reasoning is the large margin between detected concentrations and the concentrations that produce any drug effect. WHO also urged that the issue be prioritized within overall water safety management, alongside germs and other chemicals that can threaten drinking water. Our guide to WHO drinking water guidelines covers how WHO sets priorities.

EPA. There are no federal drinking water limits for pharmaceuticals. That may change:

On April 2, 2026, EPA released its draft Contaminant Candidate List 6 (CCL 6). For the first time, pharmaceuticals are listed as a priority contaminant group, alongside PFAS, microplastics and disinfection byproducts. The public comment period closed June 5, 2026. As of this writing, the list is still a draft. Being on the CCL means EPA will evaluate a contaminant for possible regulation. It doesn’t impose any requirements on water systems.
At the same time, EPA released human health benchmarks for 374 pharmaceuticals. Each benchmark is built from the drug’s lowest therapeutic dose on its FDA label, with separate values for the general population and infants. EPA says the benchmarks are not regulations and are not enforceable. They’re screening tools: levels at or below a benchmark are unlikely to cause harm, and a detection above one could prompt more monitoring or research.

What isn’t settled. Researchers note real gaps. The USGS–EPA authors describe long-term exposure to low-level mixtures as a knowledge gap, and they measured only the original drugs, not the breakdown products that form during treatment. USGS notes that the bigger documented concern is for aquatic life, such as hormone-disrupting effects on fish.

How treatment plants handle pharmaceuticals

Standard treatment removes some pharmaceuticals but not all. A USGS study of a conventional treatment plant tracked 113 organic compounds, including drugs. Of 45 detected in source water, 21 showed up in at least one finished water sample. The plant achieved “substantial but incomplete” removal. Granular activated carbon filtration accounted for 53% of the removal, chlorine disinfection for 32% and settling for 15%.

That’s consistent with what we know about the main treatment steps: coagulation and settling target particles, activated carbon targets dissolved organic chemicals, and oxidants like chlorine break some compounds down.

If you want to reduce exposure at home

You don’t need to do anything based on current evidence, but some people choose to filter. If you do:

Look for NSF/ANSI 401. This standard covers “emerging compounds/incidental contaminants,” a group of chemicals that have been detected in drinking water at trace levels. NSF’s certified product listings for 401 include claims for several pharmaceuticals, among them atenolol, carbamazepine, estrone, ibuprofen, meprobamate, naproxen, phenytoin and trimethoprim, plus non-drug chemicals like BPA and DEET.
Check the specific claim. Certification is listed contaminant by contaminant. A filter “certified to NSF 401” may not be certified for every compound on the list. Search the NSF certified product database for the exact model and claims before you buy.
Understand the filter types. Activated carbon and reverse osmosis are the technologies most often certified for these compounds. Our comparison of reverse osmosis vs. carbon filters and our NSF certification guide explain the differences.
Replace cartridges on schedule. A spent carbon filter stops adsorbing chemicals.

Keep drugs out of the water to begin with

The FDA’s recommended order for getting rid of unused medicine:

Use a drug take-back option if one is available, such as a pharmacy kiosk, police station drop-off or a prepaid mail-back envelope. This is the best choice for most medicines.
Flush only if the medicine is on FDA’s Flush List and no take-back option is available. These are drugs, including many opioids, that can be dangerous to a child or pet in a single dose. FDA says not to flush anything else.
Otherwise, use the trash. Mix pills (don’t crush them) with something unappealing like used coffee grounds or cat litter, seal the mixture in a plastic bag, and throw it away. Scratch personal information off the label.

Bottom line

Trace pharmaceuticals are real and measurable in some tap water, especially where rivers receive treated wastewater. The levels found are far below medical doses, and WHO considers the risk to people very unlikely. EPA is now formally evaluating pharmaceuticals as a group, and its new benchmarks give utilities a way to judge detections. If you want extra assurance, a filter with the specific NSF/ANSI 401 claims you care about is a reasonable choice. To see how your own water system scores on the contaminants EPA does regulate, search your ZIP code.