In older houses, hot tap water can contain small amounts of lead from the solder used to join pipes together. But even modern plumbing can leach chemicals into hot water, so the rule still applies.
Photo by Andrew Gustar
Heat makes things dissolve more readily, whether we're talking about the flavorful compounds in tea leaves, or the chemicals that make up your water pipes. Research by engineer Andrew Whelton's team has found that some brands of PEX piping release 100 times more of certain chemicals in hot water versus cold, and that some brands leach more than others. The chemicals aren't necessarily dangerous, but some can change the water's odor and taste, and others may exceed health limits set by some states. If you're the type to play it safe, stick to cold water for drinking and cooking.