Check faucets and pipes for leaks. The smallest drip from a worn washer can waste 20 or more gallons a day. Larger leaks can waste hundreds. Replace your old toilet with a low-flow toilet. Ultra low-flush toilets use no more than 1.6 gallons per flush.
Old toilets use three to six gallons per flush.
Don't use the toilet as an ashtray or wastebasket. If you have an older toilet, place an inch of sand in a quart-size bottle, fill it with water, and place it in the tank away from the operating mechanism. You can save five or more gallons a day. Take shorter showers. Install water-saving showerheads or flow restrictors.