Tiny pieces of plastic shed from food wrappers, grocery bags, clothing, cigarette butts, tires and paint are invading the environment and every facet of daily life. Researchers know the plastic particles have even made it into municipal water supplies, but very little data exists about the scope of microplastic contamination in drinking water. After years of planning, California this year is embarking on a first-of-its-kind data-gathering mission to illuminate how prevalent microplastics are in the state’s largest drinking water sources and help regulators determine whether they are a public health threat.