Radon claims a prominent place in the pantheon of household hazards, right alongside asbestos and carbon monoxide. Naturally deriving from the radioactive decay of radium in soil and rocks, this stealthy gas can enter your home through cracks in the foundation. Though less significant a risk, well water may also contain dissolved radon. Once the water reaches the air — at the end of your faucet or showerhead, for example — radon can escape into your home as a gas. Exposure to elevated levels of radon in indoor air can lead to lung cancer, posing a particular threat to people who already smoke. Drinking tap water containing radon could also prove carcinogenic, though the link to cancer has not been definitively established.

• What Is a Safe Level of Radon For Indoor Air?
  
  According to the EPA, the average indoor radon level in the United States is 1.3 picoCuries per liter (pCi/L). Levels higher than 4 pCi/L present a health hazard. But before panicking, be aware that the Radon Potential Index, a combined effort of the U.S. Geological Survey (USGS) and the Environmental Protection Agency (EPA), shows that on average, San Francisco obtains a fairly low radon risk level. So if you would like to be absolutely certain of safe radon levels in your home, your only option is to test for the presence of this colorless, tasteless and odorless gas.
  
  
• How Do You Test For Radon?
  
  Testing for radon is a fairly easy do-it-yourself job, but be sure to follow directions carefully so that you obtain accurate results. As a state resident, you can get a free short-term radon test kit compliments of the California Department of Health Services. Just call the Radon Hotline at (800) 745-7236 to place your order and obtain further information on testing. If you are purchasing a testing device from a hardware store, you can go to the EPA’s radon Web site to print a PDF document for discount coupons for both long- and short-term tests.