If your roof runoff is connected to pavement or sidewalk, re-route it to a rain barrel or cistern or dry well, or to land where the water can penetrate the ground rather than run off. Rain barrels store water that can be used for landscaping. Use a bucket to catch shower water as it warms up, then use the water for your most precious plants. Do not install automatic sprinklers. They could quintuple your water use, and that costs money.
Evaporation takes up lots of water.
Reduce your power consumption, which may require large volumes of water for power plant cooling. Maintain your septic system properly. Septic systems are the best means of keeping water local, rather than sending the water to distant wastewater treatment plants. Have them inspected annually and pumped out regularly. Make your voice heard.