Contaminants in US Drinking Water: A Reference Guide

Last updated: September 20, 2026

This page is a plain-language reference to the contaminants most often found in United States drinking water: what each one is, how it reaches the tap, what the Environmental Protection Agency (EPA) and the National Cancer Institute (NCI) say about its health effects, and whether a federal enforceable limit exists. It is written for anyone reading a water quality report, considering a well test, or trying to understand a news story about a rule change. Every factual statement links to a primary government source, and the regulatory section at the bottom carries its own "current as of" date so it can be updated separately.

Quick reference: federal limits at a glance

The table below summarizes the federal picture for each contaminant covered on this page, drawn from EPA's National Primary Drinking Water Regulations table. A maximum contaminant level (MCL) is the enforceable limit for public water systems. A maximum contaminant level goal (MCLG) is the non-enforceable health goal. Private wells are not covered by any of these limits.

Contaminant Federal enforceable limit Health goal (MCLG)
Total trihalomethanes (TTHM) 0.080 mg/L (80 ppb) None set for the group
Haloacetic acids (HAA5) 0.060 mg/L (60 ppb) None set for the group
Arsenic 0.010 mg/L (10 ppb) Zero
PFOA and PFOS 4.0 ppt each (in force; compliance required by April 26, 2029) Zero
PFHxS, PFNA, HFPO-DA (GenX) 10 ppt each (in force; rescission proposed in 2026) 10 ppt each
Lead No MCL; treatment technique with an action level of 0.015 mg/L (15 ppb), falling to 0.010 mg/L on November 1, 2027 Zero
Copper No MCL; treatment technique with an action level of 1.3 mg/L 1.3 mg/L
Nitrate (as nitrogen) 10 mg/L 10 mg/L
Radon None (a 1999 proposal was never finalized) None
Radium-226 and radium-228, combined 5 pCi/L Zero
Uranium 30 µg/L Zero
Chromium-6 (hexavalent chromium) None specific to chromium-6; total chromium is limited to 0.1 mg/L (100 ppb) 0.1 mg/L (total chromium)
Microplastics None None

Disinfection byproducts: trihalomethanes and haloacetic acids

Disinfection byproducts are chemicals created inside the water system itself, when chlorine or other disinfectants react with naturally occurring organic matter. The 2 regulated groups are total trihalomethanes (TTHM), limited to 0.080 mg/L, and 5 haloacetic acids (HAA5), limited to 0.060 mg/L. EPA associates both groups with an increased risk of cancer.

What are disinfection byproducts and how do they get into drinking water?

According to EPA's Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules page, disinfectants added to kill pathogens can react with naturally occurring materials in the water to form byproducts, including trihalomethanes, haloacetic acids, chlorite, and bromate. Unlike most contaminants on this page, they do not come from the source water; they form during treatment and in the distribution pipes. EPA's plain-English guide to the rules lists the 4 trihalomethanes as chloroform, bromodichloromethane, dibromochloromethane, and bromoform, and the 5 regulated haloacetic acids as chloroacetic, dichloroacetic, trichloroacetic, bromoacetic, and dibromoacetic acids.

What are the health effects?

EPA's regulations table lists liver, kidney, or central nervous system problems and an increased risk of cancer for TTHM, and an increased risk of cancer for HAA5. EPA's 2024 introduction to the rules describes the cancer evidence as increased rates of cancer in rodents, and adds adverse reproductive and developmental effects as potential risks of prolonged exposure. On the human side, NCI's Division of Cancer Epidemiology and Genetics reports that a study of 6 cancer sites in Iowa found associations between rectal and bladder cancer and long-term exposure (more than 40 years) to drinking water high in these byproducts. NCI describes this as an association, not an established cause.

Is there a federal limit?

Yes. TTHM is limited to 0.080 mg/L and HAA5 to 0.060 mg/L under EPA's drinking water regulations. Compliance is measured as a locational running annual average, meaning the average of the previous 4 quarters of samples at each monitoring location, as described in EPA's guide to the rules.

Arsenic

Arsenic is a naturally occurring element that reaches drinking water mainly through erosion of natural deposits into groundwater. EPA classifies inorganic arsenic as carcinogenic to humans, and the federal limit is 0.010 mg/L (10 parts per billion) with a health goal of zero.

What is arsenic and how does it get into drinking water?

Arsenic is a naturally occurring element widely distributed in the earth's crust, per the Agency for Toxic Substances and Disease Registry. EPA's regulations table lists its drinking water sources as erosion of natural deposits, runoff from orchards, and runoff from glass and electronics production wastes. NCI's arsenic fact sheet notes that inorganic arsenic is naturally present at high levels in the groundwater of certain countries, including the United States.

What are the health effects?

EPA lists skin damage, problems with circulatory systems, and a possible increased risk of cancer. EPA's Integrated Risk Information System classifies inorganic arsenic as carcinogenic to humans, with bladder cancer and lung cancer as the classified outcomes. NCI states that prolonged ingestion of arsenic-containing drinking water is associated with an increased risk of bladder cancer and skin cancer, and that cancers of the lung, digestive tract, liver, kidney, and lymphatic and hematopoietic systems have been linked to arsenic exposure.

Is there a federal limit?

Yes. The MCL is 0.010 mg/L (10 ppb), which public systems have been required to meet since January 23, 2006, according to EPA's arsenic rule history. The MCLG is zero.

PFAS (per- and polyfluoroalkyl substances)

PFAS are a class of thousands of synthetic chemicals in use since the 1940s that break down very slowly. In April 2024 EPA set the first federal drinking water limits for 6 of them, including 4.0 parts per trillion for PFOA and PFOS. Those limits remain legally in force, though EPA proposed in May 2026 to rescind 4 of the 6 and to allow more time to meet the PFOA and PFOS limits. Neither proposal has been finalized as of the date at the top of this page.

What are PFAS and how do they get into drinking water?

EPA's 2024 PFAS drinking water rule describes PFAS as a large class of thousands of synthetic chemicals in use in the United States and around the world since the 1940s. EPA's page on PFAS health and environmental risks lists drinking water as an exposure route and identifies sources that include manufacturing facilities, landfills and waste sites, and fire extinguishing foam. NCI's PFAS research page notes that PFAS are a component of firefighting foams used at airports and military installations.

What are the health effects?

In the 2024 rule, EPA cited developmental effects to fetuses during pregnancy and to breast- or formula-fed infants, an increased risk for certain cancers, and negative immunological effects for PFOA and PFOS. EPA's 2024 toxicity assessment for PFOA and its assessment summary for PFOS each classify the chemical as "likely to be carcinogenic to humans" by the oral route. EPA's general PFAS health page lists increased risk of prostate, kidney, and testicular cancers, along with immune, developmental, cholesterol, and reproductive effects. NCI reports its own studies found an increased risk of kidney cancer associated with higher PFOA exposure and of testicular cancer with PFOS, and notes that the International Agency for Research on Cancer classified PFOA as carcinogenic to humans and PFOS as possibly carcinogenic in 2023. For the other 4 regulated PFAS, EPA's 2024 rule relied on non-cancer effects on the liver, growth and development, hormone levels, kidney, immune system, lipid levels, nervous system, and reproduction.

Is there a federal limit?

Yes, since 2024. The rule, published April 26, 2024 and effective June 25, 2024, set MCLs of 4.0 ppt for PFOA, 4.0 ppt for PFOS, 10 ppt each for PFHxS, PFNA, and HFPO-DA (GenX chemicals), and a hazard index of 1 for mixtures of 2 or more of PFHxS, PFNA, HFPO-DA, and PFBS. The MCLGs for PFOA and PFOS are zero. Public water systems must complete initial monitoring by April 26, 2027 and comply with the MCLs by April 26, 2029, per the rule; EPA's rule page summarizes these as 2027 and 2029. The regulatory section below covers the 2026 proposals to change parts of this rule.

Lead and copper

Lead usually enters tap water inside the building, from corrosion of lead service lines, lead solder, and brass fixtures, rather than from the source water. EPA states there is no safe level of lead exposure. Lead has no MCL; instead, water systems must control corrosion and act when more than 10 percent of sampled taps exceed an action level of 15 ppb, a figure the Lead and Copper Rule Improvements lower to 10 ppb starting November 1, 2027.

How does lead get into drinking water?

Per EPA's basic information on lead in drinking water, lead enters water when plumbing materials that contain lead corrode, especially where the water has high acidity or low mineral content. Lead pipes are more likely in older cities and in homes built before 1986. The Centers for Disease Control and Prevention describes the same corrosion pathway.

What are the health effects?

EPA's lead information page states that even low levels of lead in the blood of children can result in behavior and learning problems, lower IQ and hyperactivity, slowed growth, hearing problems, and anemia. In pregnancy, EPA lists reduced growth of the fetus and premature birth. In adults, EPA's regulations table lists kidney problems and high blood pressure. EPA set the MCLG at zero because, in its words, the best available science shows there is no safe level of exposure to lead.

Is there a federal limit?

There is no MCL. Lead and copper are regulated through a treatment technique: systems must control corrosion and take further action, including public education and service line replacement, when more than 10 percent of tap samples exceed the lead action level of 0.015 mg/L (15 ppb). The Lead and Copper Rule Improvements, published October 30, 2024, lower the action level to 0.010 mg/L (10 ppb) and require replacement of lead service lines; EPA's compliance dates fact sheet confirms the new action level applies starting November 1, 2027. Copper shares the rule, with an action level and MCLG of 1.3 mg/L; EPA lists gastrointestinal distress from short-term exposure and liver or kidney damage from long-term exposure.

Nitrate

Nitrate reaches drinking water mainly from fertilizer runoff, septic systems, and sewage, and shallow rural wells are the most likely to be affected. The federal limit is 10 mg/L (measured as nitrogen), set to protect infants under 6 months from methemoglobinemia, often called blue-baby syndrome.

What is nitrate and how does it get into drinking water?

Nitrate and nitrite are nitrogen-oxygen compounds that occur naturally in soil, water, and some foods, per NCI's Cancer Trends Progress Report. EPA's regulations table lists runoff from fertilizer use, leaking septic tanks, sewage, and erosion of natural deposits as sources. The Agency for Toxic Substances and Disease Registry states that shallow, rural domestic wells are the wells most likely to be contaminated with nitrate, especially where nitrogen fertilizers are in widespread use. EPA notes on its nitrate in groundwater page that private, self-supplied drinking water systems are not federally regulated, which is why nitrate is a particular concern for well owners.

What are the health effects?

EPA states that infants below the age of 6 months who drink water containing nitrate above the MCL could become seriously ill and, if untreated, may die; symptoms include shortness of breath and blue-baby syndrome. EPA's private wells page names the condition methemoglobinemia, and EPA's guidance for infants on well water advises against mixing well water containing more than 10 mg/L of nitrate with infant formula or food. On cancer, NCI's progress report states that nitrate and nitrite can form N-nitroso compounds in the body, which are known to cause cancer in animals and may cause cancer in humans, and that studies have found increased risks of colon, kidney, and stomach cancer among people with higher water nitrate intake, with more modest evidence for thyroid and ovarian cancer in women.

Is there a federal limit?

Yes. Under EPA's drinking water regulations, the MCL and MCLG for nitrate are both 10 mg/L measured as nitrogen; for nitrite, both are 1 mg/L. These limits apply to public water systems only. A private well has no limit unless the owner tests it.

Radon, radium, and uranium

These 3 naturally occurring radioactive contaminants enter groundwater from uranium-bearing rock and soil. Radium and uranium have federal limits (5 pCi/L combined radium and 30 µg/L uranium). Radon does not: EPA proposed a standard in 1999 and never finalized it. Most of the risk from radon in water comes from breathing it after it escapes into indoor air during showering and other household use.

What is radon and how does it get into drinking water?

Radon is a colorless, odorless, tasteless radioactive gas produced by the natural breakdown of uranium in the ground, and it can dissolve and accumulate in groundwater such as wells, per EPA's radon in drinking water page. When water containing radon is used for showering, washing dishes, and cooking, the gas escapes into indoor air. EPA states that only about 1 to 2 percent of radon in indoor air comes from drinking water; most comes from soil beneath the building. EPA's Citizen's Guide to Radon puts it plainly: compared to radon entering through water, radon entering through the soil is usually a much larger risk.

What are the health effects?

Breathing radon causes lung cancer. EPA's radon health risk page states radon is responsible for about 21,000 lung cancer deaths every year in the United States, and NCI's radon fact sheet describes lung cancer as the only cancer proven to be associated with inhaling radon. For radon that stays in the water and is swallowed, EPA states there is a risk of internal organ cancers, primarily stomach cancer, and that this risk is smaller than the lung cancer risk from breathing it. For radium, EPA's radionuclide basics page states chronic exposure to high levels can increase the incidence of bone, liver, or breast cancer. For uranium, EPA lists increased risk of cancer and kidney toxicity in its regulations table, and its uranium page cites cancer of the bone or liver from ingesting high concentrations.

Is there a federal limit?

For radium and uranium, yes. EPA's Radionuclides Rule, published December 7, 2000, sets combined radium-226 and radium-228 at 5 pCi/L, gross alpha activity at 15 pCi/L (excluding radon and uranium), beta and photon emitters at 4 millirem per year, and uranium at 30 µg/L. For radon, no. EPA proposed a radon rule on November 2, 1999 with an MCL of 300 pCi/L, or an alternative of 4,000 pCi/L for states with an approved indoor air radon program, and the rule was never finalized. EPA's current regulations table lists no radon standard.

Chromium-6 (hexavalent chromium)

Chromium-6 occurs naturally through erosion of chromium deposits and is also released by industrial processes. There is no federal limit specific to chromium-6. The federal MCL of 0.1 mg/L (100 ppb) covers total chromium in all its forms, and it was set in 1991 on the basis of skin effects rather than cancer. EPA finalized a health assessment in 2024 that classifies chromium-6 as likely to be carcinogenic when ingested, but has not proposed a new standard.

What is chromium-6 and how does it get into drinking water?

Per EPA's chromium in drinking water page, chromium is an odorless, tasteless metallic element found naturally in rocks, plants, soil, volcanic dust, and animals. It exists mainly as trivalent chromium (chromium-3), an essential dietary element, and hexavalent chromium (chromium-6). Chromium-6 occurs naturally from erosion of chromium deposits and is also produced by industrial processes; EPA's regulations table lists discharge from steel and pulp mills alongside natural erosion.

What are the health effects?

EPA states the current total chromium standard is based on potential dermatological effects over many years, such as allergic dermatitis. EPA's Integrated Risk Information System assessment of hexavalent chromium, finalized in August 2024, classifies chromium-6 as carcinogenic to humans by inhalation and likely to be carcinogenic to humans by the oral route, which is the route that matters for drinking water. NCI's chromium fact sheet addresses workplace exposure: occupational exposure to hexavalent chromium compounds is associated with increased risks of lung cancer and cancer of the paranasal sinuses and nasal cavity. The NCI page does not address ingestion through drinking water.

Is there a federal limit?

Not for chromium-6 specifically. The MCL and MCLG for total chromium are 0.1 mg/L (100 ppb), promulgated in 1991, and that limit covers chromium-6 along with other forms. EPA lists total and hexavalent chromium among regulations under review, and in its fourth Six-Year Review, published July 23, 2024, EPA said it would consider whether the chromium standard is a candidate for revision once the health assessment was final. No proposal has followed as of the date at the top of this page.

Microplastics

Microplastics are plastic particles ranging from 5 millimeters down to 1 nanometer. There is no federal drinking water standard for them, no validated EPA analytical method for measuring them in drinking water, and, in EPA's words, significant data gaps about their health effects. In April 2026 EPA included microplastics as a group on a draft Contaminant Candidate List, describing it as a first step; the list is for study, not a decision to regulate.

What are microplastics and how do they get into drinking water?

EPA's microplastics research page defines them as plastic particles from 5 millimeters (about the size of a pencil eraser) down to 1 nanometer, with nanoplastics as the subset smaller than 1 micrometer. Primary microplastics are manufactured small; secondary microplastics come from the breakdown of larger items such as packaging, tires, and synthetic textiles. EPA states they have been found in every ecosystem on the planet and in food, beverages, and human and animal tissue. A National Institutes of Health summary of a 2024 study reported roughly 240,000 plastic particles per liter in bottled water, about 90 percent of them nanoplastics.

What are the health effects?

Neither EPA nor NCI identifies an established human health endpoint for microplastics in drinking water. In its draft Contaminant Candidate List 6, EPA states there remain significant data gaps for microplastics that will require further research before the agency can fully understand the risks, including the lack of a health-based definition identifying which particle characteristics are associated with adverse effects. NIH describes the potential health effects as still unproven and unknown.

Is there a federal limit?

No. Microplastics do not appear in EPA's drinking water regulations, and EPA's proposed sixth Unregulated Contaminant Monitoring Rule (July 1, 2026) leaves them out because there is no validated drinking water analytical method. The draft CCL 6, published April 6, 2026, includes microplastics as a contaminant group; EPA's CCL 6 page describes the list as contaminants that may require future regulation, and the Federal Register notice states that inclusion on the list does not mean a contaminant will necessarily be regulated.

The regulatory picture

This section is current as of September 16, 2026. It is maintained separately from the contaminant reference above.

Five recent federal actions bear directly on what public water systems must deliver at the tap, or on what recourse people have when they do not. Each is summarized from the primary document, followed by a short note on complications that could follow from it.

The 2024 PFAS drinking water rule

On April 26, 2024, EPA published the PFAS National Primary Drinking Water Regulation, the first enforceable federal limits for PFAS in drinking water. It set MCLs of 4.0 ppt for PFOA and PFOS, 10 ppt each for PFHxS, PFNA, and HFPO-DA, and a hazard index of 1 for mixtures of those 3 plus PFBS, with MCLGs of zero for PFOA and PFOS. The rule took effect June 25, 2024. Systems must finish initial monitoring by April 26, 2027 and meet the limits by April 26, 2029. EPA estimated that 4,100 to 6,700 water systems serving 83 to 105 million people would need to take action.

Complications: the rule is being challenged in the D.C. Circuit in American Water Works Association v. EPA, No. 24-1188, and the court's argument calendar listed the case for oral argument on September 18, 2026. A decision could uphold, vacate, or remand parts of the rule. Separately, EPA's own 2026 proposals, described next, would change 4 of the 6 standards and the compliance timeline for the other 2 if finalized.

EPA's 2026 proposals to rescind 4 PFAS limits and extend PFOA and PFOS deadlines

On May 14, 2025, EPA announced it would keep the PFOA and PFOS limits, seek to extend their compliance date to 2031, and reconsider the standards for PFHxS, PFNA, HFPO-DA, and the hazard index. The proposed rules followed on May 20, 2026. The rescission proposal (91 FR 29413) would remove the MCLs, MCLGs, and related monitoring provisions for PFHxS, PFNA, HFPO-DA, and the hazard index mixture; it does not touch PFOA or PFOS. The compliance extension proposal (91 FR 29425) would let eligible systems request an extension of the PFOA and PFOS compliance date from April 26, 2029 to April 26, 2031, keep the 4.0 ppt limits and the 2027 monitoring deadline in place, and require systems granted an extension to notify the people they serve. Comment periods on both closed July 20, 2026. As of the date on this section, neither has been finalized, and all 6 standards from the 2024 rule remain legally in force with their original deadlines.

Complications: until a final rule is published, water systems are planning against 2 possible sets of requirements. If the rescission is finalized, monitoring for PFHxS, PFNA, HFPO-DA, and PFBS would no longer be required under the federal rule, though states may keep their own standards. The extension, as proposed, is request-based rather than automatic, so compliance dates could differ from one system to the next. Any final rule could itself be challenged, and the outcome of the pending D.C. Circuit case on the 2024 rule could change what there is to rescind.

The Lead and Copper Rule Improvements

EPA published the Lead and Copper Rule Improvements on October 30, 2024 (89 FR 86418), effective December 30, 2024, with a compliance date of November 1, 2027. The rule requires water systems to replace all lead service lines and certain galvanized lines under their control within 10 years of the compliance date, with a limited deferred-deadline exception for systems with a high proportion of lines to replace, subject to state approval. It lowers the lead action level from 0.015 mg/L to 0.010 mg/L, removes the lead trigger level, requires first- and fifth-liter samples at homes with lead service lines with the higher value used for compliance, and requires systems to maintain service line inventories and notify customers annually until a lead line is replaced. EPA's rule page and an August 21, 2026 implementation guidance release describe the rule as in effect without any change to its dates; as of the date on this section, no Federal Register action modifying it has been published.

Complications: the rule is also before the D.C. Circuit, in American Water Works Association v. EPA, No. 24-1376, with oral argument listed on the court's argument calendar for September 30, 2026. Until the compliance date, the 15 ppb action level continues to apply, so a system can be in compliance today at a level that would trigger action in 2027. The 10-year replacement clock does not start until November 1, 2027, and the deferred-deadline exception means some systems could take longer. The replacement requirement covers service lines under the water system's control; arrangements for privately owned portions vary.

Sterling v. City of Jackson: no constitutional right to clean drinking water

On September 4, 2026, the full U.S. Court of Appeals for the Fifth Circuit decided Sterling v. City of Jackson, No. 24-60370, a class action by residents of Jackson, Mississippi over lead-contaminated municipal water. The residents brought substantive due process claims under 42 U.S.C. § 1983 (bodily integrity and state-created danger) against the city, current and former city officials, and an engineering contractor, along with state-law tort claims. By a 10 to 5 vote, the en banc court affirmed dismissal of the constitutional claims, stating that "it is undisputed that the Constitution does not guarantee clean water" and declining to "expand the Fourteenth Amendment to create novel theories of constitutional liability." The majority also stated that the individual city officials would be entitled to qualified immunity. It affirmed dismissal of the state-law claims without prejudice, leaving them available in state court. The decision vacated a November 2025 panel ruling that had allowed the bodily integrity claim to proceed. A partial dissent by 5 judges would have found a plausible bodily integrity claim.

Complications: the ruling is binding precedent in the Fifth Circuit (Texas, Louisiana, and Mississippi) and does not change any drinking water standard or any water system's obligations under the Safe Drinking Water Act. It narrows one avenue of federal relief for residents harmed by contaminated municipal water in those states; the court left the state-law claims available to be refiled. A petition to the U.S. Supreme Court is possible; none had been filed as of the date on this section.

Sackett v. EPA and Clean Water Act jurisdiction

On May 25, 2023, the U.S. Supreme Court decided Sackett v. EPA, No. 21-454, a Clean Water Act case. All 9 justices agreed the Sacketts' property was not subject to federal permitting, and a 5 to 4 majority adopted a new test: the Act covers only wetlands with a continuous surface connection to a relatively permanent body of water connected to traditional navigable waters, such that the 2 are, as a practical matter, indistinguishable. Four justices concurred in the judgment but rejected the continuous surface connection test. The decision concerns the Clean Water Act, which governs discharges into surface waters; it does not interpret the Safe Drinking Water Act and did not change any drinking water standard. EPA and the Army Corps issued a conforming rule on September 8, 2023, proposed a new definition of "waters of the United States" on November 20, 2025, and published a supplemental proposal on September 9, 2026 with comments due October 9, 2026. No final rule has been published, and EPA's implementation page describes the operative definition as the January 2023 rule as amended by the conforming rule, or the pre-2015 regime where the 2023 rule is enjoined.

Complications: the connection to the tap is indirect. Wetlands and small streams that fall outside federal jurisdiction after Sackett may still be regulated by states, and coverage now varies by state. Where it does not, discharges to those waters are governed by state law alone, and the source waters that public systems draw from downstream could be affected over time. Because the definition is still being rewritten, the practical boundary of federal coverage may shift again when a final rule is published.

What you can do

Read your utility's Consumer Confidence Report

If you are on a public water system, your utility must send you a Consumer Confidence Report every year by July 1, per EPA's consumer information page. It lists which regulated contaminants were detected, at what levels, and against what limit. Under the 2024 revisions to the rule, systems serving more than 10,000 customers will deliver the report twice a year starting in 2027. If you cannot find yours, call your utility or EPA's Safe Drinking Water Hotline at 1-800-426-4791.

If you are on a private well, test it

Roughly 15 percent of the US population relies on private wells, and EPA's private wells page is direct about it: the quality and safety of drinking water from private domestic wells are not regulated by the federal government under the Safe Drinking Water Act. EPA's guidance for well owners recommends testing annually for total coliform bacteria, nitrate, total dissolved solids, and pH, testing more often if small children, older adults, or a pregnant or nursing person live in the home, and testing immediately if local groundwater problems are known or conditions near the well change. EPA's home water treatment guide also recommends that well water be tested periodically by a state-certified laboratory; your state or local health department can tell you which additional contaminants, such as arsenic, uranium, or radon, are common in your area.

Know what a filter does and does not remove

No single home treatment method addresses every contaminant on this page. EPA's home water treatment guide summarizes the main types: activated carbon filters improve taste and odor and can remove some organic contaminants, including some disinfection byproducts, but do not remove nitrate, bacteria, or dissolved minerals; reverse osmosis forces water through a membrane and removes many dissolved inorganic and organic contaminants, with some units also reducing nitrate; distillation removes nitrate, bacteria, dissolved solids, most organic compounds, heavy metals, and radionuclides; and ion exchange softeners address hardness. EPA's PFAS home filter page adds that activated carbon, reverse osmosis, and ion exchange can reduce PFAS, and advises checking the packaging for certification to NSF/ANSI 53 or NSF/ANSI 58 for PFAS reduction. Whatever the type, EPA notes that filters are only effective if they are maintained according to the manufacturer's instructions, and it recommends choosing treatment after reading your Consumer Confidence Report or well test rather than before.

Rius Water offers reverse osmosis filtration systems for the home. We encourage you to compare any system, including ours, against your own water report and the certifications listed on the product, and to ask us if you are unsure what a given system is certified to reduce.

Sources

All sources were accessed on September 16, 2026.

This page is educational reference material and is not medical or legal advice. Limits, rules, and court decisions change; the dates on this page indicate when each section was last checked against its sources.