There are few government agencies more central to daily life in Los Angeles than the Metropolitan Water District of Southern California, which spends billions of dollars each year ensuring that 19 million people have enough to drink, in part by importing hundreds of billions of gallons from the Colorado River and Northern California. There are also few agencies more prone to bitter power struggles. The latest drama could reach a tipping point Monday, when Metropolitan’s board will consider firing the agency’s general manager — with potentially huge consequences for our water supplies, depending on whom you ask.