Toilets use a lot of water. Pay attention to the gallon per flush and EPA WaterSense ratings when buying a toilet.

Photograph by Constant/Shutterstock

Updated by James Robertson

for National Geographic

Shopping Tips

Toilets account for nearly 26 percent of water consumption in the home, and older models use far more water than newer designs. If the bathroom fixtures in your home were installed prior to 1992, replacing your toilet with a more efficient one could save thousands of gallons of water annually—between 14,000 and 25,000 gallons for a family of four

  • Gallons per Flush: Toilets are rated based on their gallons per flush (gpf). Low-flow toilets, using 1.6 gpf or less, are now the federal standard. High-efficiency toilets use 1.3 gpf, and others use as little as 1.1 gpf. Dual-flush toilets have two gpf rates (solids are flushed at the higher 1.6 gpf rate, while liquids use 1.1 gpf or less).

    Composting toilets contain and control the composting of human and household waste using little or no water at all, saving you the nearly 30 percent of household water generally used to flush toilets. The trade-off with composting toilets is that some require energy, while traditional toilets use none at all. A Texas state government analysis found that some models use 2 to 3 kilowatt-hours per day.

    No-mix toilets have different areas for solid and liquid waste. The bowl is split into two sections: the front area of the toilet collects urine, and the back section collects solid waste and works like a normal flush toilet. The toilets use separate piping for each type of waste, and store urine for use as fertilizer later. No-mix toilets are being used in Europe (especially Switzerland), but haven't caught on in the U.S. yet.

  • EPA WaterSense Ratings: The U.S. Environmental Protection Agency (EPA)'s WaterSense label requires toilets to be independently tested to show that they use, at most, 1.28 gpf and that they can successfully flush 350 grams of test media. Dual-flush toilets, those that have a full-flush mode for solids and a reduced-flush mode for liquids, must use 1.6 gpf and .8 gpf respectively (the combined average flush rate for these toilets is 1.28 gpf).
  • Maximum Performance (MaP) Testing: Maximum Performance Testing is a collaborative program between the Canadian Water and Wastewater Association and the California Urban Water Conservation Council, which tests the ability of a toilet model to completely remove solids in a single flush. The program determines the maximum amount, in grams, that a model can effectively remove, and recommends that all models be capable of removing at least 250 grams of solids
  • Matching Parts: High-efficiency toilets are often sold in two parts. When shopping, be sure that the model numbers on the tank and the bowl match.

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