Also known as low-flow toilets, water-saving toilets use 1.6 gallons of water per flush (gpf) or less, compared with older toilets that use 3.5, 5 and even 7 gpf. The 1.6-gpf models significantly reduce the amount of fresh water used and the corresponding amount of wastewater generated. For example, using a 1- to 1.6-gpf toilet instead of 3.5-gpf models cuts indoor water use by more than 15 percent; when used instead of a 5-gpf toilet, it cuts water use by 20 percent to 25 percent.
Water-saving toilets were introduced in the 1970s, and some have been notoriously poor performers, requiring multiple flushes to remove waste completely. Often those early models weren't engineered specifically to use less water but were simply modifications of existing conventional toilet designs. By contrast, the high-performing low-flow toilets available today are engineered to use less water and use it more powerfully. They remove waste at least as efficiently as conventional toilets while using much less water.
A variety of high-performing low-flow toilets is available. Following is a look at the types of technology and some of their benefits and drawbacks:
- Gravity-assisted toilet. When the toilet is flushed, the flapper valve in the tank allows water to flow from the tank into the bowl, where gravity pulls the water and waste down. Gravity-assisted models are typically the least expensive type of low-flow toilets, and they’re able to work with low water pressure. A drawback is that they have the weakest flush.
- Dual-flush gravity-assisted toilet. This toilet, which also uses gravity to remove waste, offers two flushing options. With the press of a button, you can choose a full flush of 1.6 gallons to remove solid waste or a half-flush of 0.8-gallon to remove liquid waste. While these have great water-saving potential, dual-flush toilets are the most expensive type of water saver.
- Pressure-assisted toilet. The line pressure of water entering the toilet tank compresses trapped air within a sealed tank until air pressure equals water pressure. When the toilet is flushed, the pressure of the compressed air reinforces the normal gravity flow, which works particularly well to remove waste with low amounts of water. Pressure-assisted toilets can be noisy, expensive, and require frequent repairs, however.
- Vacuum-assisted toilet. Flushing this toilet activates vacuum chambers in the tank that act like a siphon to pull water into the bowl. This design allows water to reach a greater area in the bowl, which keeps the bowl cleaner than other types of low-flow toilets do. The vacuum-assisted toilet is quieter than pressure-assisted toilets, but the flush is weaker.