Common Water Contaminants in U.S. Drinking Water
Understanding what contaminants may be in your tap water is the first step to protecting your family's health. Learn about the most common water contaminants, their sources, health effects, and how to remove them.
Contaminant Categories
Microorganisms
Bacteria, viruses, and parasites that can cause illness
Disinfectants
Chemicals added to kill microorganisms
Disinfection Byproducts
Chemicals formed when disinfectants react with organic matter
Inorganic Chemicals
Metals and minerals from natural deposits or industrial discharge
Organic Chemicals
Carbon-based compounds from industrial processes or agriculture
Radionuclides
Radioactive elements from natural sources or human activities
High Priority Contaminants
These contaminants pose the greatest health risks and require immediate attention
Lead
EPA Maximum Limit:
0.015 mg/L
Common Sources:
Lead pipes, plumbing fixtures, solder in water lines, especially in homes built before 1986
Health Effects:
Brain damage and developmental delays in children, kidney problems, high blood pressure in adults
How to Remove:
Reverse osmosis or certified lead removal filters
Arsenic
EPA Maximum Limit:
0.01 mg/L
Common Sources:
Natural deposits in rock, industrial waste, agricultural runoff
Health Effects:
Increased cancer risk, skin damage, cardiovascular disease, diabetes
How to Remove:
Reverse osmosis or anion exchange filters
Nitrate
EPA Maximum Limit:
10 mg/L
Common Sources:
Agricultural fertilizers, animal waste, septic systems, sewage
Health Effects:
Blue baby syndrome in infants, thyroid issues, increased cancer risk
How to Remove:
Reverse osmosis or ion exchange filters
PFOA (Forever Chemicals)
EPA Maximum Limit:
0.000004 mg/L
Common Sources:
Industrial discharge, firefighting foam, non-stick cookware manufacturing
Health Effects:
Cancer, liver damage, immune system effects, developmental issues
How to Remove:
Activated carbon or reverse osmosis certified for PFAS
PFOS (Forever Chemicals)
EPA Maximum Limit:
0.000004 mg/L
Common Sources:
Industrial discharge, firefighting foam, stain-resistant products
Health Effects:
Cancer, thyroid disease, pregnancy complications, immune system effects
How to Remove:
Activated carbon or reverse osmosis certified for PFAS
Chromium
EPA Maximum Limit:
0.1 mg/L
Common Sources:
Industrial discharge, natural deposits, steel and pulp mills
Health Effects:
Cancer (hexavalent chromium), allergic reactions, skin issues
How to Remove:
Reverse osmosis or ion exchange
Radium
EPA Maximum Limit:
5 pCi/L
Common Sources:
Natural deposits in rock formations
Health Effects:
Cancer, bone damage from radiation exposure
How to Remove:
Reverse osmosis or ion exchange
Medium Priority Contaminants
Monitor these contaminants and consider filtration if levels are elevated
Total Trihalomethanes (TTHMs)
EPA Maximum Limit:
0.08 mg/L
Common Sources:
Chlorine disinfection byproducts formed when chlorine reacts with organic matter
Health Effects:
Increased cancer risk, liver and kidney problems, reproductive effects
How to Remove:
Activated carbon filters
Haloacetic Acids (HAA5)
EPA Maximum Limit:
0.06 mg/L
Common Sources:
Chlorine disinfection byproducts
Health Effects:
Increased cancer risk, reproductive and developmental effects
How to Remove:
Reverse osmosis or activated carbon
Copper
EPA Maximum Limit:
1.3 mg/L
Common Sources:
Copper pipes, corrosion of plumbing
Health Effects:
Gastrointestinal distress, liver and kidney damage at high levels
How to Remove:
Reverse osmosis or distillation
Lower Priority Contaminants
Generally less concerning but may affect taste or have effects at very high levels
Fluoride
EPA Maximum Limit:
4 mg/L
Common Sources:
Natural deposits, water fluoridation, industrial discharge
Health Effects:
Dental and skeletal fluorosis at high levels, thyroid effects
How to Remove:
Reverse osmosis or activated alumina
Chlorine
EPA Maximum Limit:
4 mg/L
Common Sources:
Added as disinfectant by water utilities
Health Effects:
Taste and odor issues, potential respiratory irritation
How to Remove:
Activated carbon filters
Understanding EPA Limits
The EPA sets Maximum Contaminant Levels (MCLs) for drinking water contaminants under the Safe Drinking Water Act. Here's what you need to know:
MCL (Maximum Contaminant Level)
The highest level of a contaminant allowed in drinking water. MCLs are enforceable standards set as close to health goals as feasible using the best available treatment.
MCLG (Maximum Contaminant Level Goal)
The level at which no known or anticipated adverse health effects occur, with an adequate margin of safety. MCLGs are non-enforceable health goals.
Important Caveat
EPA limits don't necessarily mean "safe" - they represent what's technologically and economically feasible. Many scientists argue limits should be lower for contaminants like lead and PFAS.
Vulnerable Populations
Infants, pregnant women, elderly, and immunocompromised individuals may be more sensitive to contaminants even at levels below EPA limits.
How to Protect Your Family
Check Your City's Water Report
Search for your city on our site to see which specific contaminants have been detected in your water supply and at what levels.
Get the Right Filter
Choose a water filter certified to remove the specific contaminants in your water. Look for NSF/ANSI certifications that match your needs.
Test Your Home Water
Municipal testing doesn't include contamination from your home's plumbing. Consider testing for lead if you have older pipes.
Stay Informed
Read your utility's annual Consumer Confidence Report and sign up for water quality alerts in your area.
Contaminant Deep Dive Guides
Comprehensive guides covering health effects, EPA limits, testing, and removal methods
Lead
Brain damage, developmental delays
PFAS
Forever chemicals, cancer risk
Arsenic
Cancer, cardiovascular disease
Nitrates
Blue baby syndrome, thyroid issues
Chromium-6
Carcinogen, lung damage
Bacteria
E. coli, coliform, waterborne illness
Copper
Gastrointestinal, liver damage
Pesticides
Hormonal disruption, cancer
Chlorine
Taste/odor, disinfection byproducts
Fluoride
Dental/skeletal fluorosis at high levels
Microplastics
Emerging contaminant, research ongoing
Pharmaceuticals
Trace medications in water supply
How to Test Your Water
Complete guide to testing your tap water for contaminants, choosing the right test, and understanding your results.