Less than 1 percent of recent drinking water samples at California’s public schools showed elevated lead levels. But thousands more campuses still need to be tested, state officials said last week. A new law, AB 746, took effect in January requiring those tests at public schools over the next 16 months. Lead exposure can affect nearly every system in the body, and because it often has no obvious symptoms, it frequently goes unrecognized, the U.S. Centers for Disease Control and Prevention reported. Childhood exposure to lead has been shown to affect IQ, ability to pay attention and academic achievement.