San Francisco Chronicle: Drought, population growth, global warming, a collapsing Sacramento-San Joaquin River Delta environment – it’s no secret that California’s water challenges are only going to get more challenging in the near future. So you’d think, at the very least, that the state would measure how much water farmers – who use about 80 percent of the water drawn from the ailing delta – use each year. And you’d best think again. There’s no system to measure or monitor how much of our water is …