Who gets California’s water, and how much, is a high-stakes affair, and it’s based on a system of water rights born long ago, when the West was wild — and often unfair. The first-come, first-served pecking order established during European settlement gave the new and dominant landowners first dibs on pumping rivers and creeks. The beneficiaries, which include the likes of San Francisco and its pristine supplies in Yosemite, continue to enjoy tremendous advantage, consuming water with little constraint while others sometimes go without. Amid growing water shortages and focus on equity, the system has begun drawing increased scrutiny. Last week the state Legislature weighed in with the unusual step of advancing measures that would help regulators rein in the most privileged and profligate water users.