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Written by
Michael Torres
Michael Torres
Last updated: March 14, 2026
American tap water meets some of the strictest safety standards in the world — but “safe” doesn’t mean “pure.” The EPA regulates over 90 contaminants, yet hundreds of unregulated chemicals, microplastics, and emerging pollutants are routinely detected in drinking water nationwide.
This guide lists every major contaminant category found in US tap water, where they come from, their health effects, and which filtration technologies remove them.
Regulated Contaminants Found in Tap Water
Disinfectants and Disinfection Byproducts
The most common contaminants in city water are the very chemicals used to make it safe:
| Contaminant | EPA Limit (MCL) | Source | Health Effects | How to Remove |
|---|---|---|---|---|
| Chlorine | 4 mg/L | Added as disinfectant | Skin/eye irritation, taste/odor | Carbon filter |
| Chloramine | 4 mg/L | Added as disinfectant | Same as chlorine, harder to remove | Catalytic carbon |
| THMs (trihalomethanes) | 80 ppb | Chlorine + organic matter | Liver/kidney damage, cancer risk | Carbon or RO |
| HAAs (haloacetic acids) | 60 ppb | Chlorine + organic matter | Cancer risk | Carbon or RO |
| Bromate | 10 ppb | Ozone + bromide | Cancer risk | RO |
Chlorine and chloramine are intentionally added and considered safe at EPA levels. The concern is their byproducts — THMs and HAAs — which form when chlorine reacts with natural organic matter. These byproducts are the main reason many people choose to filter city water.
Ozone treatment produces far fewer byproducts than chlorination, which is one of the key benefits of ozone water treatment.
Heavy Metals
| Metal | EPA Limit | Source | Health Effects | How to Remove |
|---|---|---|---|---|
| Lead | 15 ppb (action level) | Old pipes, solder, fixtures | Brain damage (children), kidney damage | Carbon block, RO |
| Copper | 1,300 ppb | Corroding copper pipes | Stomach/intestinal distress | RO, ion exchange |
| Arsenic | 10 ppb | Natural deposits, industrial waste | Cancer, cardiovascular disease | RO, specialty media |
| Mercury | 2 ppb | Industrial discharge, natural deposits | Kidney damage, nervous system | Carbon, RO |
| Chromium-6 | 100 ppb (total chromium) | Industrial discharge, natural deposits | Cancer (at any level per research) | RO, ion exchange |
Lead is the most widespread heavy metal concern. An estimated 6–10 million US homes still connect to water mains through lead service lines. See our guide to the best water filters for lead removal.
Inorganic Chemicals
| Chemical | EPA Limit | Source | Health Effects | How to Remove |
|---|---|---|---|---|
| Fluoride | 4 mg/L | Added for dental health, natural deposits | Skeletal fluorosis (high levels) | RO, bone char, activated alumina |
| Nitrate | 10 mg/L | Fertilizer runoff, septic systems | Blue baby syndrome (infants) | RO, ion exchange |
| Barium | 2 mg/L | Natural deposits, drilling waste | Cardiovascular effects | RO, ion exchange |
| Cyanide | 200 ppb | Industrial discharge | Nervous system damage | RO, chlorination |
Emerging Contaminants (Unregulated or Newly Regulated)
PFAS (“Forever Chemicals”)
PFAS are the most significant emerging water contaminant. Over 12,000 PFAS compounds exist, but the EPA only set limits for 6 in 2024:
- PFOA: 4 ppt (linked to kidney cancer, testicular cancer)
- PFOS: 4 ppt (linked to thyroid disease, immune suppression)
- GenX (HFPO-DA): 10 ppt
- PFHxS: 10 ppt
- PFNA: 10 ppt
- PFBS: Included in hazard index calculation
An estimated 200+ million Americans have PFAS in their drinking water. The best removal methods are reverse osmosis and activated carbon (carbon block, not GAC). See our best water filters for PFAS removal.
Microplastics
Studies have found microplastics in 94% of US tap water samples. These tiny plastic particles (under 5mm) come from degrading plastic waste, synthetic clothing fibers, and industrial processes.
- Not yet regulated by EPA
- Health effects: Still being studied — potential hormone disruption, inflammation
- How to remove: Carbon block filters, RO systems, or ceramic filters with pore sizes under 1 micron
Pharmaceuticals
Trace amounts of medications are regularly detected in tap water:
- Antibiotics, hormones (estrogen, testosterone), antidepressants, painkillers
- Enter water supply through human excretion, improper drug disposal, and agricultural runoff
- Concentrations are typically very low (parts per trillion) but effects of chronic exposure are unknown
- How to remove: Carbon filters (NSF 401 certified), RO systems
Pesticides and Herbicides
| Chemical | EPA Limit | Source | How to Remove |
|---|---|---|---|
| Atrazine | 3 ppb | Agricultural runoff | Carbon filter |
| Glyphosate | 700 ppb | Agricultural runoff | Carbon filter, RO |
| 2,4-D | 70 ppb | Herbicide runoff | Carbon filter |
| Chlordane | 2 ppb | Legacy contamination | Carbon filter |
Biological Contaminants
| Organism | EPA Limit | Source | Health Effects | How to Remove |
|---|---|---|---|---|
| Total coliform | 0 (5% of samples) | Soil, animal waste | Indicates possible contamination | UV, ozone, chlorine |
| E. coli | 0 | Human/animal waste | Severe gastrointestinal illness | UV, ozone, chlorine |
| Giardia | 99.9% removal required | Animal waste, contaminated water | Diarrhea, cramps (giardiasis) | UV, ozone, 1-micron filter |
| Cryptosporidium | 99% removal required | Animal waste | Severe diarrhea, potentially fatal for immunocompromised | UV, ozone, 1-micron filter |
| Legionella | 0 | Building water systems | Legionnaires’ disease (pneumonia) | UV, ozone, heat (140°F+) |
City water is disinfected, so biological contamination is rare. Well water has no such protection — annual bacteria testing is essential. Both UV and ozone water treatment are effective chemical-free disinfection methods. Ozone is particularly effective against Cryptosporidium, which resists chlorine. Learn more about how ozone purifies water.
Contaminants by Water Source
| Contaminant Type | City Water | Well Water |
|---|---|---|
| Chlorine/chloramine | Common (added) | None |
| Disinfection byproducts | Common | None |
| Lead | Depends on plumbing age | Depends on plumbing age |
| PFAS | Common | Possible (near contamination sources) |
| Bacteria | Rare (disinfected) | Common risk |
| Nitrates | Monitored/treated | Common (agricultural areas) |
| Iron/manganese | Low (treated) | Very common |
| Hydrogen sulfide | Rare | Common (rotten egg smell) |
| Pesticides | Monitored/treated | Possible (agricultural areas) |
| Hardness minerals | Varies by region | Often high |
For a detailed comparison, see our well water vs city water filtration guide.
What You Can Do About It
- Test your water — Use our water testing guide to identify what’s actually in your water
- Choose the right filter — Match your contaminants to the right technology using our complete filtration guide
- Consider chemical-free options — UV and ozone treatment remove contaminants without adding chemicals
- Replace filters on schedule — An expired filter can release trapped contaminants back into your water. See our filter replacement guide
FAQ
Is US tap water safe to drink?
For most people, yes. US tap water meets EPA safety standards, and waterborne disease outbreaks are rare. However, “safe” means below regulatory limits — not contaminant-free. Some people choose to filter for additional peace of mind, especially for lead, PFAS, and disinfection byproducts.
Which US cities have the worst tap water?
Water quality varies within cities, not just between them. Areas with older infrastructure (pre-1986 plumbing), agricultural runoff exposure, or proximity to industrial sites tend to have more contamination. Rather than relying on city rankings, test your own tap water — it’s the only way to know what you’re drinking.
Does boiling water remove contaminants?
Boiling kills bacteria and viruses but does NOT remove chemical contaminants. In fact, boiling concentrates chemicals like lead, PFAS, and nitrates because water evaporates but contaminants remain. Only use boiling for boil-water advisories related to bacteria.
Are there contaminants the EPA doesn’t test for?
Yes. The EPA regulates ~90 contaminants, but over 86,000 chemicals are used in the US, and many end up in water supplies without regulation. The EPA’s Unregulated Contaminant Monitoring Rule (UCMR) periodically tests for emerging contaminants, but new regulations take years to implement.
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About the Author
Michael Torres
Water Treatment Engineer · Last updated: March 14, 2026Michael Torres is a certified water treatment engineer with over 15 years of experience evaluating ozone and advanced oxidation systems. He reviews commercial and residential pool equipment and reports on system performance across facilities in North America.
