Use efficiency laws

From Water Wiki

During the 1950's and 60's, toilets used 7.0 g/f then were reduced to 3.5 g/f in the 80's.

In 1995 the National Energy Policy Act (H.R. 776) went into effect and mandated 1.6 gallons/flush toilets for the entire U.S. This conservation requirement is reflected in the NC Plumbing code which regulates the flow and consumption of toilets (1.6 gallons/flush), urinals (1.0 gallons/flush), shower heads (2.5 gallons/minute), lavatory (2.2 g/m - private, .5 g/m for public), and sink faucets (2.2 g/m).  International plumbing code/NC Plumbing Code has adopted this standard. 

This change represents a 75% decrease in toilet water usage and even further reduction is possible. In fact, dual flush toilets are 20% more efficient than the 1.6 gallon/flush toilets.

Under the EPA's WaterSense standards for water conservation, certified toilets are required to flush with no more than 1.28 gallons per flush, a 20% savings from existing standards.