Low-flow toilets use a fraction of the water to flush compared with older models -- 1.6 gallons per flush, as opposed to the 7 gallons outdated toilets use. If you buy a new toilet today, it will be a low-flow toilet, since 1.6 gallons per flush is the federally mandated maximum, according to 1992’s Energy Policy Act. Installing low-flow toilets is environmentally friendly, and you will begin realizing significant savings on your water bills immediately.