As the drought drags on, South Coast agencies are scrambling to lay the groundwork for a potable water supply that might one day be the region’s largest, after Lake Cachuma: purified and recycled wastewater. For the past 25 years, a small amount of wastewater from sinks, tubs, and toilets has been treated and sprayed on the turf at golf courses, schools, and parks in Santa Barbara and the Goleta Valley. It’s not suitable for drinking, but it keeps the grass green.