According to the Pacific Institute, toilets are the single biggest water-consuming fixture in most homes and offices. Further, much of this water - nearly a trillion gallons - could be saved each year through the use of high-efficiency toilets.   
The following data about how much water American toilets use - and could save - every year is provided by Waterless Co.:   
• According to the Plumbing Manufacturer's Institute, there are 225 million toilets in the U.S.   
• The average toilet is flushed five times per day.  
• Toilets manufactured before 1980 generally used six gallons per flush (gpf), or about 11,000 gallons per year.   
• Toilets manufactured between 1980 and 1994 generally used 3.5 gpf, or 6,388 gallons per year.   
• Most toilets manufactured after 1994 are considered to be "low-flow" toilets, and generally use 1.6 gpf, or 2,920 gpf annually.   
• High-efficiency toilets (HETs) use about 1.3 gpf, or 2,372 gallons annually.   
• Replacing an old toilet with an HET can reduce water usage by 78 percent.    
• About half the toilets in the U.S. are considered inefficient, meaning they consume more than 1.6 trillion gallons of water per year.
• About half the toilets in the U.S. are considered efficient, meaning they use 1.6 gpf, or only 460 billion gallons of water or less per year.

"If everyone in the U.S. installed an efficient or high-efficiency toilet, we would be saving more than a trillion gallons of water per year," says Niki Bradley, marketing manager for Waterless Co. "That's enough water to fill two million Olympic-sized swimming pools with potable, drinkable water."