Water contaminants

What each contaminant is, why it matters in measured EPA/CDC terms, and the certification that actually removes it.

• Lead

  If you are worried about lead, here is the thing to know first: it usually is not coming from your water source, it is picked up on the way to your tap. Lead leaches in from corrosion of older lead service lines, plumbing, and brass fixtures, so it is the pipes in and around your home that matter most. That is why two houses on the same supply can test completely differently, and why your neighbor's result does not tell you yours.

• PFAS (PFOA / PFOS)

  PFAS are a large family of long-lasting synthetic chemicals (the 'forever chemicals' you have probably seen in the news), used in nonstick and waterproof products. The reason they keep coming up is that they do not break down easily, so they persist in the environment and have turned up in many public water supplies. If you are on a system that has reported them, this is the one worth taking seriously.

• Chlorine and Chloramine

  If your water smells faintly like a swimming pool, this is usually why. Utilities add chlorine or chloramine on purpose, to disinfect drinking water and keep it safe all the way through the distribution system. What is left over by the time it reaches you - the residual - is what you taste and smell at the tap.

• Volatile Organic Compounds (VOCs)

  VOCs are a broad group of carbon-based chemicals - the name stands for volatile organic compounds. Some come from industrial or agricultural runoff, others form as byproducts of the disinfection process itself, and any of them can end up in drinking water. The key thing to hold onto is that 'VOCs' is a whole category, not a single substance.

• Nitrate

  If you are on a private well, especially in farm country, this is the one to put on your radar. Nitrate enters drinking water mainly from fertilizer runoff, animal manure, and septic systems, so it shows up most in agricultural areas and in wells. The catch is that it gives no warning - no taste, no smell, no color - so the only way to know is to test.

• Arsenic

  Arsenic sounds alarming, but the practical story is simpler than the name: it is a naturally occurring element that dissolves into groundwater from rock and soil, and it can also come from industrial or agricultural sources. It turns up most in private wells and in some regional aquifers, and like nitrate it gives no clue at the tap - it is tasteless and colorless, so testing is the only way to know.

• Hard Water (Hardness)

  If you are fighting chalky spots on glasses or crust on the showerhead, hard water is almost certainly the culprit. Hard water simply means water high in dissolved calcium and magnesium, minerals it picks up moving through limestone and rock. That is what leaves scale on fixtures and appliances, spotting on dishes, and that stubborn feeling where soap will not lather.

• Fluoride

  Fluoride is one people feel strongly about, so here is the plain version. It occurs naturally in groundwater, and many U.S. utilities also add it on purpose (community water fluoridation) to reduce tooth decay. Levels vary widely depending on your source, and most people cannot taste it - so whether you want to reduce it is genuinely your call to make.

• Chromium-6 (Hexavalent Chromium)

  You may know this one already without the chemistry name: hexavalent chromium (chromium-6) was the contaminant at the center of the Hinkley, California case made famous by Erin Brockovich. It enters drinking water from industrial discharge and some natural deposits, and like arsenic and nitrate it is tasteless and colorless, so you cannot detect it without testing.

• Mercury

  Mercury is a naturally occurring heavy metal, and the practical thing to know is where it comes from: it can dissolve into groundwater and surface water from natural mineral deposits, discharge from refineries and factories, and runoff from landfills and croplands. Because it carries no taste, color, or smell, you will not notice mercury in tap water yourself - laboratory testing is the only way to find it.

• Microplastics

  Microplastics are exactly what they sound like - tiny plastic particles, generally measured down to about 0.5 microns (a micron is a thousandth of a millimeter, far too small to see). They reach tap water from things like the breakdown of larger plastic debris, synthetic fibers, and packaging, and they can hang on as water moves through pipes and treatment systems. Worth knowing for what comes next: they are counted as physical particles, not as a dissolved chemical.

• Cysts (Cryptosporidium and Giardia)

  Cysts are the dormant, shelled form of two waterborne parasites, Cryptosporidium and Giardia (the bugs behind many "stomach flu" outbreaks traced to water). They get into drinking water through fecal contamination from humans or animals, often when surface water carrying runoff, sewage, or agricultural waste reaches a supply. The reason they matter is that tough outer shell: it lets the organism survive in water for a long time and shrug off the standard chlorine that handles most germs.

• Pharmaceuticals and Emerging Compounds

  This category sounds unsettling but the amounts are key to the story. Pharmaceuticals and emerging compounds are trace residues of medicines and everyday products that end up in source water - drugs like ibuprofen and naproxen, the hormone estrone, the plasticizer bisphenol A, and the insect repellent DEET. They reach rivers, lakes, and groundwater mainly through wastewater, because neither the human body nor conventional sewage treatment fully breaks them down. The amounts are very small, measured in nanograms per liter (a nanogram is a billionth of a gram).

• Asbestos

  Asbestos in water tends to surprise people, but the source is mundane: it is a group of naturally occurring mineral fibers, and in drinking water it most often comes from the corrosion of older asbestos-cement water mains and from natural mineral deposits the water moves through. The fibers are microscopic and do not change the taste, color, or smell - so, as with the other invisible ones, testing is how you would know.

• Copper

  Like lead, copper is something your home adds on the way to the faucet, not something in the source water. It leaches from copper plumbing, soldered joints, and brass fittings inside household and building systems, and you will see the most of it in water that has sat in the pipes overnight. Soft or acidic water tends to dissolve a bit more copper from whatever plumbing it touches - so a first-thing-in-the-morning glass is the worst case.