City officials struck a deal today that could save Angelenos 3 billion gallons of water a year. For more than a decade, L.A. has poured water into the mostly dried-up Owens Lake, 200 miles northeast. The water stops huge amounts of dust from blowing out of the salty lake bed and polluting the air. It’s also a kind of penance paid by Los Angeles for diverting the Owens River away from the lake in the first place, 100 years ago. Now, after years of negotiations, water officials in L.A. and the Owens Valley have agreed on an alternative plan for controlling the dust.