Half the Water, Twice the Flush!

Enlarge Image Image Gallery Compared with older models, low-flow toilets save the average U.S. household (2.64 people) about 25 gallons of water per day, or more than 9,000 gallons per year. MATTHEW T. STALLBAUMER

If the toilets in your home are from the mid-1990s or earlier, consider installing new ones to save big on your water bills. All new models are “low-flow” toilets — by law they can use no more than 1.6 gallons of water per flush. Prior to 1994, most toilets on the market used at least 3.5 gallons, or about 20 gallons of water per person per day — the most water used by any household appliance. What a waste! Not only did this add to your water bills, but as recent droughts and water shortages remind us, clean water is a resource we need to conserve. Low-flow toilets now save the average U.S. household (2.64 people) about 25 gallons of water per day, or more than 9,000 gallons per year (according to the book Water Use and Conservation by Amy Vickers).

But while some low-flow models work well, others do not. That’s because to comply with the federal regulations on toilets’ water use, some manufacturers initially reduced the volume of water that discharges from the tank, without also making the necessary design adjustments. New designs have improved the performance of many models, but some still do not flush thoroughly. For a list of the best of the best, see "The Best Low-flow Toilets," below.

Kinds of Toilets

To be an informed shopper, it helps to know the two basic kinds of toilets available on the market.

Gravity-flush toilets. These are conventional toilets for residential use that have been engineered to use less water. When you press the knob, a flush valve opens and the water in the tank drains into the bowl through rim openings and a siphon jet. The force of the water pushes the waste through the trap and down the drainpipe. While they are usually less effective at removing solid waste than pressure-assist toilets (described below), gravity-flush toilets are generally less expensive and easier to maintain, because most use standard parts.

Pressure-assist toilets. Best suited for commercial use or in homes with poor drainpipe carry, these models use the pressure of the water supply to the toilet to compress air in an inner tank. When you flush the toilet, pressurized water is forced into the bowl, blasting waste down the drainpipe. Pressure-assist toilets have a distinctive whoosh sound that’s much louder than gravity-flush toilets, but they are more effective in removing solid waste.