It turns out that mothers the world over are right: Don’t drink the shower water. Lynn Kirby, a water quality engineer for Seattle Public Utilities, recommends “not using hot water for drinking or cooking” for two primary reasons: the potential for bacterial growth in the hot water heater tank, and because “hot water tends to corrode pipes more quickly than cold water, so you may get more dissolved metals from the hot water tap compared to the cold.”
The biggest concern is lead. Although lead solder was banned in the United States in 1987, there are still millions of lead-soldered copper pipes that haven’t been replaced. Hot water running through these pipes can cause the lead to leach out. The Environmental Protection Agency calls lead solder “the major cause of lead contamination of household water in U.S. homes today.” The only way to know if your water contains lead is to have it tested. The Centers for Disease Control and Prevention lay out how to determine what steps to take, and the National Safety Council recommends buying a commercial lead test or consulting the nonprofit corporation Clean Water Lead Testing Inc. for a mail-order lead test.
Heat from the hot water tank will also tend to dissipate the residual chlorine in the water, says Kirby, which “could result in the growth of bacteria in the hot water tank.” But, like the potential for lead exposure, there’s no way of determining if the bacteria are actually harmful (or exist) unless you test the water. So slake your thirst outside the shower.