Common Water Contaminants

While municipal water treatment removes many contaminants, your tap water may still contain trace amounts of various substances. According to the EPA, over 90 contaminants are regulated in public drinking water, but many more can potentially be present without specific standards.

This guide covers the most common contaminants found in American drinking water, including their sources, health effects, regulatory limits, and effective removal methods. Understanding these contaminants helps you make informed decisions about your water quality.

Sources

Lead rarely comes from source water. Instead, it typically enters drinking water through:

• Lead service lines: Pipes connecting water mains to homes, especially in cities built before 1950
• Lead solder: Used to join copper pipes until banned in 1986
• Brass fixtures: Faucets and valves can contain up to 8% lead (pre-2014) or 0.25% (current standards)
• Lead pipes inside homes: Common in homes built before 1950

The Flint, Michigan water crisis demonstrated how changes in water chemistry can cause massive lead leaching from existing infrastructure.

Health Effects

According to the CDC and EPA, there is no safe level of lead exposure:

• Children: Developmental delays, learning difficulties, lower IQ, behavioral problems, hearing damage, slowed growth
• Pregnant women: Reduced fetal growth, premature birth
• Adults: Cardiovascular effects, increased blood pressure, kidney damage, reproductive problems

Lead accumulates in the body over time, so even low-level chronic exposure is harmful.

How to Remove Lead

• NSF 53-certified carbon filters: Can reduce lead by 97%+ (must be specifically certified for lead)
• Reverse osmosis: Removes 95-99% of lead
• Distillation: Highly effective
• Flush your pipes: Run cold water for 30-60 seconds before drinking, especially in the morning
• Use cold water: Hot water leaches more lead from pipes

Learn more in our detailed Lead in Drinking Water Guide.

Why They're in Your Water

Chlorine and chloramines serve a critical purpose: preventing waterborne disease outbreaks. Before chlorination became widespread in the early 1900s, diseases like cholera, typhoid, and dysentery killed thousands of Americans annually.

• Chlorine: The traditional disinfectant, effective and inexpensive. Dissipates relatively quickly.
• Chloramine: A combination of chlorine and ammonia. More stable, lasting longer in distribution systems. Used by about 20% of US water utilities.

Health Effects

At regulated levels, chlorine and chloramine are considered safe, but some concerns exist:

• Taste and odor: The most common complaint; some people are more sensitive than others
• Skin and eye irritation: May affect sensitive individuals, especially during bathing
• Respiratory effects: Steam from hot showers can release chlorine gas
• Disinfection byproducts: The bigger concern is that chlorine reacts with organic matter to form DBPs (see below)

Disinfection Byproducts (DBPs)

When chlorine or chloramine reacts with organic matter in water, it creates byproducts including:

• Total Trihalomethanes (TTHMs): MCL of 80 ppb. Includes chloroform and related compounds.
• Haloacetic Acids (HAA5): MCL of 60 ppb. A group of five related acids.

According to the EPA, long-term exposure to high levels of DBPs may increase cancer risk and cause liver, kidney, and central nervous system problems.

How to Remove

• Activated carbon filters: Excellent for removing chlorine and improving taste (NSF 42 certified)
• Catalytic carbon: Better for chloramine removal than standard carbon
• Letting water sit: Chlorine will dissipate in 24 hours if left in an open container (does not work for chloramine)
• Whole-house carbon filters: Remove chlorine from all water, including shower water

Sources

• Natural occurrence: Fluoride is present in groundwater in many areas, sometimes at high levels
• Water fluoridation: About 73% of US public water systems add fluoride to prevent tooth decay
• Industrial sources: Aluminum and phosphate fertilizer manufacturing

Health Effects

Fluoride at optimal levels (around 0.7 mg/L) is considered beneficial for dental health. However:

• Dental fluorosis: At levels above 2 mg/L, children may develop white spots or staining on teeth
• Skeletal fluorosis: Very high long-term exposure (above 4 mg/L) can cause bone problems
• Some studies suggest: Potential effects on thyroid function and neurodevelopment at higher exposures, though research is ongoing

How to Remove

Standard carbon filters do NOT remove fluoride. Effective options include:

• Reverse osmosis: Removes 90-95% of fluoride
• Activated alumina: Specifically designed to remove fluoride
• Bone char carbon: A specialized type of carbon effective for fluoride
• Distillation: Removes essentially all fluoride

Sources

• Agricultural runoff: The primary source, from fertilizer application on crops
• Animal waste: From feedlots, dairies, and other concentrated animal operations
• Septic systems: Can leach nitrates into groundwater
• Natural sources: Some nitrates occur naturally from decomposing organic matter

Nitrate contamination is most common in agricultural regions of the Midwest, Central Valley of California, and other farming areas.

Health Effects

• Pregnant women: Should limit exposure; some studies suggest links to birth defects and pregnancy complications
• Adults: Generally more tolerant, but high chronic exposure may affect thyroid function and increase certain cancer risks

How to Remove

Standard carbon filters do NOT remove nitrates. Effective options include:

• Reverse osmosis: Removes 85-95% of nitrates
• Ion exchange: Specifically designed to remove nitrate ions
• Distillation: Effective for nitrate removal

Never boil water to remove nitrates. Boiling concentrates nitrates, making them more dangerous.

What Are PFAS?

Per- and polyfluoroalkyl substances (PFAS) are a group of over 9,000 synthetic chemicals used since the 1940s for their water-resistant, non-stick, and stain-resistant properties. They're called "forever chemicals" because they don't break down in the environment or in the human body.

Sources

• Firefighting foam (AFFF): Used extensively at airports, military bases, and fire training facilities
• Industrial facilities: Manufacturing plants that use or produce PFAS
• Landfills: Consumer products in landfills can leach PFAS into groundwater
• Wastewater treatment plants: Cannot effectively remove PFAS
• Products: Non-stick cookware, waterproof clothing, food packaging, stain-resistant carpets

Health Effects

According to the EPA and research studies, PFAS exposure has been linked to:

• Increased risk of certain cancers (kidney, testicular)
• Thyroid disease and hormone disruption
• Immune system effects, including reduced vaccine response
• Liver damage
• Developmental effects in infants and children
• Increased cholesterol levels
• Reproductive problems

How to Remove

PFAS are challenging to remove and require specific technologies:

• Reverse osmosis: Most effective home treatment, removing 90-99% of PFAS
• Activated carbon (granular): Can reduce PFAS 60-90% depending on contact time and carbon type
• NSF P473 certified filters: Specifically tested and certified for PFAS reduction
• Ion exchange resins: Effective for some PFAS compounds

Standard pitcher filters are generally NOT effective for PFAS removal unless specifically certified.

Learn more in our comprehensive PFAS Forever Chemicals Guide.

Sources

• Natural deposits: The primary source in most cases, especially in the Western United States
• Mining and smelting: Historical and ongoing mining operations
• Agricultural runoff: From some pesticides and herbicides
• Industrial discharge: Electronics manufacturing, wood preservation

High-risk areas include Arizona, Nevada, California, and other Western states with volcanic geology.

Health Effects

The EPA classifies arsenic as a Group A human carcinogen. Long-term exposure can cause:

• Skin, bladder, and lung cancer
• Skin changes and lesions
• Cardiovascular disease
• Diabetes
• Reproductive effects
• Developmental effects in children

Even at the legal limit of 10 ppb, lifetime exposure carries some cancer risk. Health advocates have pushed for a stricter limit.

How to Remove

Standard carbon filters do NOT remove arsenic effectively. Options include:

• Reverse osmosis: Removes 95-99% of arsenic
• Adsorption media: Iron-based media designed specifically for arsenic
• Distillation: Highly effective
• Ion exchange: Can be effective for certain forms of arsenic

Types of Microorganisms

Bacteria

• Total Coliforms: Indicator bacteria that suggest potential fecal contamination
• E. coli: Specifically indicates recent fecal contamination
• Legionella: Causes Legionnaires' disease; thrives in warm water systems

Parasites

• Giardia: Causes giardiasis (beaver fever); relatively common in surface water
• Cryptosporidium: Highly chlorine-resistant; caused the 1993 Milwaukee outbreak affecting 400,000 people

Viruses

• Norovirus: Highly contagious; causes gastroenteritis
• Hepatitis A: Can be transmitted through contaminated water

Sources

• Sewage contamination: From leaking sewer lines or septic systems
• Agricultural runoff: Animal waste entering water sources
• Wildlife: Animals defecating near water sources
• Treatment failures: Inadequate disinfection at treatment plants
• Distribution system problems: Pipe breaks, cross-connections

Health Effects

• Acute gastroenteritis: Nausea, vomiting, diarrhea, cramps
• More serious infections: Depending on the pathogen and individual health
• Immunocompromised individuals: Can experience severe or life-threatening illness

How to Remove

• Boiling: Kill pathogens by boiling for 1 minute (3 minutes above 6,500 ft elevation)
• UV purification: Kills 99.99% of bacteria, viruses, and parasites
• Reverse osmosis: Physically removes microorganisms
• NSF 53 certified filters: For cyst reduction (Giardia, Cryptosporidium)
• Chlorine/iodine treatment: Effective for most bacteria and viruses (not all parasites)

Well water users should test annually for bacteria. See our Private Well Water Testing Guide.

What Is Hard Water?

Hard water contains high concentrations of dissolved minerals, primarily calcium and magnesium. The USGS classifies water hardness as:

• Soft: 0-60 mg/L (calcium carbonate equivalent)
• Moderately hard: 61-120 mg/L
• Hard: 121-180 mg/L
• Very hard: Over 180 mg/L

Sources

Calcium and magnesium dissolve into groundwater as it passes through limestone, dolomite, and other mineral-rich rock formations. Hard water is more common with groundwater sources.

Effects

Hard water minerals are not health hazards and may even provide dietary minerals. However, they cause:

• Scale buildup: White deposits on fixtures, in pipes, and appliances
• Reduced appliance efficiency: Scale buildup in water heaters reduces efficiency and lifespan
• Soap scum: Soap doesn't lather well and leaves residue
• Dry skin and hair: Some people notice skin and hair effects
• Spotty dishes: Mineral deposits on glassware

How to Treat

• Water softeners (ion exchange): Replace calcium and magnesium with sodium or potassium ions
• Reverse osmosis: Removes minerals along with other contaminants (for drinking water)
• Polyphosphate treatment: Prevents scale formation without removing minerals
• Magnetic/electronic conditioners: Claimed to alter mineral behavior; effectiveness is debated

Note: Water softeners add sodium to your water, which may be a concern for people on low-sodium diets. Potassium-based softeners are an alternative.

Several other contaminants are frequently found in drinking water:

Key: Green = Effective | Yellow = Partially effective or requires specific certification | Red = Not effective