The math is simple. An old-style toilet can use up to six gallons of water to complete the flush cycle. Today's low-flow toilets use one and a half gallons. Multiply the number of people in your family or the total number of toilet visits a year and it can add up to 4,000 wasted gallons of water. So what kind of toilet system should you consider?
Low Flow If you want basic energy efficiency in the bath, start with low-flow models. These have been on the market now for the most amount of time. They use around 1.5 gallons of water per flush.
Single flush high-efficiency toilets (HET) You'll find more than 60 manufacturers producing Single flush HETs today. Depending on the model, you'll use between 0.8 and 1.28 gallons per flush.
Dual-flush HETs The dual flush model HET lets you choose between a 0.8 gallon flush for liquid-only waste or a heavier 1.6 gallon flush for normal operations.
Narrowing your choices for bathroom efficiency
Start by downloading the comparison chart for maximum toilet performance at The Alliance for Water Efficiency. You can view brand names, models, HET performance and more.
The calculations are based on Maximum Performance (MaP) Testing, as system developed in 2003 by plumbing and water-efficiency specialists in the United States and Canada. The current tests evaluate 2,050 different tank-type toilets on the market as well as the more than 1,000 tank-type WaterSense-certified high-efficiency toilets.
WaterSense is a program by the U.S. Environmental Protection Agency that evaluates and promotes consumer knowledge in water conservation and products. The EPA claims that WaterSense labeled toilets can save you 4,000 gallons of water a year,or up to $90 on your water bill.
View manufacturer or retail store websites
You can also make comparisons by visiting home improvement stores or fixture retailers to measure features and prices. For example, Lowe's has online charts of their high-performance toilets by American Standard, Crane, Jacuzzi and Kohler. Finally, if you're really interested in the WaterSense certification standards, you can read them in their entirety.
I didn't mention prices, but you'll discover that HET models come across the full price range and you're sure to find one that you can afford.