If you have municipal water, ask the utility for a copy of its latest water analysis.  Federal law requires most public water companies to have the water tested regularly and to make the results available for inspection.  The test results tell the condition of the water when it left the reservoir or treatment plant.  Reports won't describe the condition at your tap.  Remember, lead generally leaches into the water from household plumbing.

If you draw your water from a private well, call the local public health department to find out if any groundwater problems exist.  If you drink well water, you should have it tested periodically for bacteria, inorganic compounds, and radon.  Test for organic chemicals if the well is within a mile or two of a gasoline station or refinery, a chemical plant, a landfill, or a military base.  If you live in an agricultural area, have the water tested for nitrate and pesticides.  Test for lead if your house is more than 30 years old or if the plumbing pipes are joined with lead solder.

Where to go for tests … Companies that sell water-treatment equipment often offer a free or low-cost water analysis as part of the sales effort.  Don't depend on this kind of test: it’s like asking a barber if you need a haircut.  Consult an independent, state-certified lab instead.  You can often find one in the Yellow Pages under "Laboratories -Testing."

Mail-order labs:  
These labs send you a kit containing collection bottles, mailers and detailed instructions.  You collect water samples and ship them by overnight package delivery.  The labs provide test results and an explanation of the numbers two to three weeks later. 

If a test report says your water has an especially high level of a contaminant like lead, nitrate, or radon, have the water tested by a second lab before taking costly remedial action.