Consider purchasing a low-volume toilet that uses less than half the water of older models.
Install a toilet displacement device to cut down on the amount of water needed to flush, however don’t use a displacement device if you use a low flow toilet.
Place a 1-gallon plastic jug of water into the tank to displace toilet flow (do not use a brick, it may dissolve and loose pieces may cause damage to the internal parts). Be sure installation does not interfere with the operating parts.
Replace your showerhead with an ultra-low-flow version.
Place a bucket in the shower to catch excess water for watering plants.
Avoid flushing the toilet unnecessarily. Dispose of tissues, insects, and other similar waste in the trash rather than the toilet.
Avoid taking baths by taking short showers. Turn on water only to get wet and lather and then again to rinse off.
Avoid letting the water run while brushing your teeth, washing your face, or shaving.