Water-saving flushers can save hundreds of gallons of water over their lifetime, but only if your plumbing system can handle the switch in fixtures.
Builders of older houses assumed toilets would always flush more than 3 gallons of water to carry away waste, not the misery 1.6 gallons today’s toilets use. So there’s a chance that plumbing in an older home simply can't work with that relative trickle.
Waste drains beneath the toilet need to slope between 1/8-in. and 1/4-in. per foot for the water to carry solid waste to the sewer. If they’re too steep or too level, the flow of water allows waste to collect in the pipe and that means clogs. Some old houses, for reasons of age or builder error, may even have a “negative slope” where water stands in the pipe. Waste is carried away only by the force of gallons of water flowing through the system courtesy of an older toilet.
Don’t be too worried, though. The average home plumbing system will work fine with today’s low-flow toilets. Just watch out for a couple of danger signs:
Whatever new toilet you choose, look for one carrying the WaterSense label. These typically are 20 percent more water-efficient than average products in their category. What does that mean to you? The U.S. EPA calculates that replacing a single pre-1980 toilet with one measuring up to WaterSense standards can save an average family 18,000 gallons of water and $110 in utility costs.