Drinking Water Contaminants: Complete Guide
Filtering your water without knowing what's in it is guesswork. The wrong filter for the wrong contaminant is the same as no filter at all — and the water filter industry counts on you not knowing the difference. These 16 guides cover what each contaminant is, where it comes from, the health evidence, and which NSF certifications actually verify removal. Start with what's most likely in your source water, or test first and filter what you find.
PFAS (Forever Chemicals)
Severe
PFAS are synthetic chemicals with carbon-fluorine bonds so stable they persist indefinitely in the environment and body. EPA's 2024 rule sets the MCL at 4 ppt for PFOA and PFOS.
Lead
Severe
Lead enters drinking water almost entirely through aging plumbing — the source water is typically lead-free. The EPA action level is 15 ppb, but EWG recommends 1 ppb as the health goal.
Chlorine
Low Risk
Chlorine is added by municipalities to kill bacteria and viruses. It's effective and regulated, but causes taste/odor issues and forms THMs. Activated carbon removes it easily.
Fluoride
Moderate
Fluoride is intentionally added to ~70% of US municipal water supplies. Standard carbon filters do not remove it — reverse osmosis, distillation, and activated alumina are effective.
Arsenic
Severe
Arsenic is a naturally occurring metalloid common in well water in western and New England states. The EPA limit of 10 ppb is 250x higher than EWG's recommended health guideline.
Chromium-6 (Hexavalent Chromium)
High Risk
Chromium-6 (immortalized in the Erin Brockovich case) contaminates water in all 50 states. There is no specific federal MCL — it falls under the total chromium standard. California has proposed stricter limits.
Nitrates
High Risk
Nitrates are common in rural well water, particularly in agricultural regions. They're a top concern for households with infants under 6 months. Reverse osmosis removes 83–92% of nitrates.
Microplastics
Moderate
Microplastics have been detected in tap water, bottled water, and even human blood. While long-term health effects are not yet established, precautionary filtration is advised.
Bacteria & Viruses
Severe
Biological contamination is the primary concern for private well owners. Municipal water is chlorinated to kill pathogens, but wells have no treatment unless homeowners add it themselves.
Pharmaceuticals
Low Risk
Pharmaceuticals are detected in trace amounts in many US water supplies but are not regulated under the Safe Drinking Water Act. Current research suggests low acute risk; long-term effects are understudied.
Radium
High Risk
Radium contamination is most common in water from deep wells, particularly in the Midwest and Southeast. It is odorless, tasteless, and colorless — only laboratory testing detects it.
Copper
Moderate
Unlike lead, copper is an essential nutrient at low levels but becomes toxic above the EPA action level of 1.3 mg/L. Most exposure comes from corroded copper pipes in older homes.
Disinfection Byproducts (DBPs)
Moderate
DBPs form when chlorine reacts with organic compounds in source water. They're highest in summer (warmer water, more organic matter). Activated carbon removes 90%+ of THMs.
Hydrogen Sulfide
Low Risk
Hydrogen sulfide causes the distinctive rotten-egg smell in well water. While not a significant health risk at typical residential concentrations, it corrodes copper plumbing and makes water unpleasant.
Iron & Manganese
Moderate
Iron and manganese are common in private well water. They cause orange/brown staining, metallic taste, and laundry discoloration. Iron filters using oxidation, greensand, or KDF media are the standard treatment.
Chloramine
Low Risk
Chloramine is used by ~30% of US utilities as a longer-lasting disinfectant that produces fewer THMs. However, it forms different DBPs (N-nitrosamines) and requires catalytic carbon for removal — regular activated carbon is ineffective.