How to improve the quality of water within local communities

For several years, California has had a statewide drought that not only reduced the amount of water we use throughout the Central Valley to the point farms relied on groundwater to irrigate crops, but also the quality of our water. The reliance on groundwater has led to not only overuse but also contamination from pollutants. Nitrates from agricultural runoff from farms are one of the abundant pollutants in the Central Valley as well as arsenic. Dairies seem to prefer nitrate-based fertilizers for their corn crops which pollutes ground water. Yet we have abundant biomass from which fertilizers can be made such as grape pomace, cow manure, eggshells, and coffee grounds.