California now limits every household to 100 gallons of water per day ~ barely enough for the usual household chores, but with zero allowed for watering the yard, washing the car, or topping off the swimming pool. Many other western states are contemplating similar water restrictions due to an ongoing drought.
One way to lower water consumption is with a high-efficiency toilet. They use half the water to flush. Some models have two flushing levels (further reducing water usage), one for liquid waste and another for solid waste.
Older toilets, manufactured before 1980, use 5-8 gallons per flush (GPF) ~ 50 gallons per day; half your allowed volume in California. Toilets built to 1992 standards use about 2 gallons per flush. High-efficiency toilets use 1 gallon or less.