Reuse fish tank water. Use fish tank water on your household plants. This will provide a nice fertilizer as well as save water. Don't run water before plugging and filling up the bathtub. Shower instead of bathing.
Showers usually use less water than tub baths.
Shower for less time. Even when washing hands, don't let the water run. Wet hands, turn off the water while soaping and scrubbing, and turn it on again to rinse. Use a moisture meter to determine when your house plants need a drink. More plants die from over-watering than from being on the dry side.