Request a Consumer Confidence Report (CCR) from your water district. Municipalities are now required to send these to homeowners yearly. This report will tell you about the water that is coming to your house.

Run some tap water into a clear glass and look closely at it in good lighting. Is it clear or discolored? Do you see sediment in the water? Smell the water; expect a faint smell of chlorine (like a swimming pool) if you are on a city water supply, but any other smell - particularly that of rotten eggs - indicates that your water should be tested. Check drains, fixtures and porcelain items such as toilets and tubs for red, green, blue or brown staining.

Ask the local health department or Cooperative Extension Service (part of the U.S. Department of Agriculture) for the name of a reputable local water-quality testing facility. If you live in a municipality, your water will be of a consistent quality; you won't need to have it tested every year.

Alternatively, buy a home water test from a hardware store. While less accurate than a lab test, it's a less expensive alternative.

Be especially conscious of your water quality if you have a private water supply, such as a well. You alone are responsible for your water. Test well water for herbicides and insecticides when you first move in, and then at least twice that first year (early spring and late fall) for coliforms (bacteria) and nitrates, and once a year for lead, pH and total dissolved solids (TDS). If you do any work on your well, notice chemical use on or near your property, or see any of the above-mentioned indicators, have your water checked.

Have the water tested when you move into a new home so that you will have a baseline guide for future water testing. Check for coliforms, calcium, copper, iron, lead, magnesium, nitrates, pH, sodium, sulfate, zinc and TDS.
Tips & Warnings
Sometimes just-poured tap water is cloudy from air bubbles. This cloudiness should clear within a minute or two and isn't anything to be concerned about.