“Many dangerous contaminants cannot be smelled, tasted, or seen,” says Erik Olson, a drinking-water expert with the environmental watchdog Natural Resources Defense Council. So how do you know if your water is safe? If you use public water, check your water provider’s Consumer Confidence Report, compiled by the EPA (found at www.epa.gov/safewater/ccr1.html). If you have a private well or a particular reason to suspect your water, such as long-term nausea or diarrhea, Olson says to get a state-certified home test from your local health department. Test for coliform bacteria (such as E. coli), says Chad Czarkowski, a water expert at Wisconsin’s Department of Natural Resources (coliform bacteria can indicate that water contains pathogens or intestinal parasites). Olson also recommends annual lead tests, particularly if you have children under seven. If you have a well and are pregnant or nursing, or have a child under six months, test for nitrates that sometimes leach from fertilizers and septic systems, too, since they may be fatal to infants.