Know what's in your water.
Plain-English guides to the contaminants most common in DC-metro tap water: what they are, the health context, and what actually removes them.
PFAS “Forever Chemicals”
PFAS (per- and polyfluoroalkyl substances) are a family of thousands of synthetic chemicals used in nonstick cookware, waterproof fabrics, food packaging, and firefighting foam. They earn the nickname “forever chemicals” because their fluorine-carbon bonds barely break down, so they persist in the environment and accumulate in the human body.
Read the guide →Lead
Lead is a potent neurotoxin with no known safe level of exposure, especially for infants and children. In drinking water it typically doesn't come from the source water itself. It leaches from aging infrastructure: lead service lines, older plumbing, solder, and fixtures on the way to your tap.
Read the guide →Chloramines & Disinfection Byproducts
To stop waterborne disease, utilities disinfect drinking water with chlorine or chloramine (chlorine combined with ammonia). This is essential and saves lives, but there's a tradeoff: the disinfectant reacts with natural organic matter in the water to form disinfection byproducts (DBPs), most notably total trihalomethanes (TTHMs) and haloacetic acids (HAA5).
Read the guide →Nitrates & Nitrites
Nitrates and nitrites are compounds that enter drinking water mainly through agricultural fertilizer runoff, septic systems, and wastewater discharge. They're more common in agricultural areas and in homes on private wells, but they can appear in municipal supplies too.
Read the guide →Hexavalent Chromium (Chromium-6)
Hexavalent chromium, or chromium-6, is a metal that enters water both naturally, by dissolving out of rocks and soil, and from industrial pollution such as metal plating, manufacturing, and corrosion control. It's the same contaminant made famous by the Erin Brockovich case in Hinkley, California.
Read the guide →Arsenic
Arsenic is a naturally occurring semi-metal found in the earth's crust. It enters drinking water mainly by dissolving out of rock and soil into groundwater, and can also come from past industrial and agricultural use. It is most common in private wells and in certain aquifers.
Read the guide →Radium & Radionuclides
Radium and other radionuclides, including uranium and radon, are naturally radioactive elements that dissolve into groundwater from the rock and soil it passes through. Levels depend heavily on local geology and are highest in some wells and groundwater-fed systems.
Read the guide →Copper
Copper mostly enters drinking water the same way lead often does: not from the source, but by leaching from copper pipes, brass fittings, and fixtures as water sits in your home's plumbing. Corrosive or acidic water and long standing time raise how much dissolves in.
Read the guide →Chlorine Taste & Odor
If your tap water smells like a swimming pool, that's the disinfectant working. Utilities add chlorine or chloramine (chlorine combined with ammonia) and keep a small residual in the pipes to stop bacteria from growing on the way to your home. It's essential for safety, but that residual is what you taste and smell.
Read the guide →The gap between what's legal and what's healthy
A utility can pass every federal test and still deliver water far above the levels health scientists consider safe. Federal legal limits were largely set decades ago; the health-based guidelines below reflect current cancer- and development-risk research.
Federal law allows 71× the health guideline
Federal law allows 2,500× the health guideline
Federal law allows 533× the health guideline
Federal law allows 600× the health guideline
Not federally regulated, no legal limit at all
No level is considered safe
No level is considered safe
Federal law allows 100× the health guideline
Sources: EPA National Primary Drinking Water Regulations (legal limits) and the EWG Tap Water Database / state public-health goals (health-based guidelines). A reverse osmosis system reduces every contaminant above at the point of use.
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