Check your tap water quality by zip code

The DMV's 5 worst tap water contaminants

1. 1

   Trihalomethanes (TTHMs)

   Formed when chlorine meets organic matter in treated water. Linked to cancer and pregnancy problems.

   Over EWG's guideline in 48 of 49 water systems.

   Worst: 397× in Clarke County, VA

2. 2

   Haloacetic acids (HAAs)

   The other big family of disinfection byproducts. Linked to cancer.

   Over EWG's guideline in 47 of 49 water systems.

   Worst: 841× in Prince George's County, MD

3. 3

   Radium

   Naturally occurring and radioactive. Increases cancer risk over years of drinking it.

   Over EWG's guideline in 35 of 49 water systems.

   Worst: 54× in Kent County, MD

4. 4

   Nitrate

   From fertilizer and septic runoff. Linked to cancer and harmful to infants.

   Over EWG's guideline in 29 of 49 water systems.

   Worst: 32× in Carroll County, MD

5. 5

   Chromium-6

   The "Erin Brockovich" chemical. A likely carcinogen, with no federal limit of its own.

   Over EWG's guideline in 27 of 49 water systems.

   Worst: 56× in Carroll County, MD

Times over EWG's health guideline, which is stricter than the legal limit. Source: EWG Tap Water Database, one system per county and town on the map.