Is it possible to drink too much?

Possible, but not probable. Overhydration gets a lot of press, but it’s usually the result of marathon runners who “water load,” fraternity pledges who are force-fed liquids, or partyers who have taken Ecstasy, which can spur extreme thirst while suppressing signals of satiety. In a healthy, moderately active person, Heinz Valtin, M.D., a kidney specialist and a professor emeritus at Dartmouth Medical School, says, “the body’s water-balance system is so sensitive and accurate that water intoxication is highly unlikely.”

How safe is tap water?

Generally, it’s very safe. The U.S. has some of the cleanest drinking water in the world, and 9 out of 10 public water systems meet federal health and safety standards, according to the Environmental Protection Agency (EPA). But that doesn’t mean you should be complacent. The quality of water varies depending on its source, treatment, and delivery system, as well as the plumbing it flows through, so you’d be wise to learn about what’s coming out of your tap, says Steven Patch, Ph.D., an authority on drinking-water safety and the director of the Environmental Quality Institute at the University of North Carolina in Asheville.

Patch suggests you read the water-quality report that your utility is required by law to release each year. Large providers are also required to post their reports online. Go to your water utility’s website or to the EPA’s site (www.epa.gov/safewater), which has links to scores of local water-quality reports.

Should you test your water?

Even if the report is reassuring, you might want to test your water for lead and arsenic, both of which are potentially harmful to your or your children’s health. Lead contamination can come from the plumbing in people’s homes (most often in houses built before 1986), so it isn’t accurately represented in water-quality reports. Arsenic is common in both well water and municipal water collected from wells, says Patch.

If you’re worried about unregulated contaminants — if there’s a factory upstream, for instance, or someone in your household has a weak immune system— you might want to test for microorganisms and other pollutants, says Erik Olson, the lead author of a study conducted by the Natural Resources Defense Council (NRDC), an advocacy group that tested the drinking water in 19 U.S. cities. If you find your water has contaminants, contact your local water carrier. (See Local Drinking Water Information Resources for companies that sell home test kits.)