All week, we’ve been looking at how our relationship to water will likely change in the hotter, drier, more populous California of the year 2040. Today, we look at water rights; who can use water and how much. Much of California’s arcane system of water rights stretches back to the Gold Rush. Basically, people who first claimed access to a water source have the first right to use it. It’s a seniority based system: older claims trump younger ones when water is scarce. But can a 19th Century approach to water allocation survive in the 21st Century?