In the next 18 months, a small plane will fly over every city in California, recording data on what kind of plants are growing in our lawns, parks and street medians. That data will help determine where we’re wasting water, and help cities use it more efficiently. It’s a radical departure from the way water conservation has been done in California in the past, when, during water emergencies, state officials would simply instruct cities to cut usage by a certain percentage.