Deep soaks of about 1 inch once or twice a week are best. This practice encourages deep root growth, which promotes a healthy lawn. Taller grass blades provide shade to the roots and reduce water loss from evaporation. Aerating your lawn will help water reach the roots. Add water slowly to your vegetable garden, using a small droplet size.
Large droplets tend to compact soil, making it difficult for roots to become well established.
Most sprinklers are intended for lawns, not gardens, and tend to over apply water causing nutrients to be leached from the soil. Consider installing a drip system to slowly deliver water directly to individual plants. When washing the car, try using a bucket of soapy water and a hose with a shut-off nozzle. By reducing the amount of water used to wash the car, you will also reduce the amount of soapy rinse water going to storm drains and area streams. Clean gutters and downspouts by hand, instead of using a hose.