Plants and turf are healthier if you water them in accordance with their needs. Turfgrass and ornamentals develop deeper and stronger root systems with proper watering. Native or adapted plants usually require less maintenance.
Proper irrigation means less run-off of fertilizer.
If it flows down the street, it's not helping your plants. Less water for irrigation may mean a lower water bill. Steady or increased river flows Overall decreased water use and a drop in peak water use mean forestalling or avoiding mean a healthier river and bay aquatic community.