High-Efficiency, water saving toilets
High-Efficiency toilets are toilet that use even less water than the federally mandated 1.6 gallons per flush. They are also called Low-flow toilets of low-flush toilets. These toilets came into existence as a response to a national program created by the US Environmental Protection Association (EPA) in 2006. They created the WaterSense Program; with the goal of reducing water used in flushing with another 20%. This led to a maximum flush of 1.28 gallons. Since 2006, the states California, Georgia, Texas, and Colorado have adopted the EPA standard of 1.28 gallons per flush. Selling toilets with larger flushing capacity in these states is not allowed. Other states are considering legislation of the WaterSense EPA standard.
As you might expect these High-Efficiency toilets have to be very powerful to flush well with such low volumes of water. The first designs that came on the markets were mostly traditional toilets with adjusted flushes. There were often not powerful enough and required multiple flushes (with no water saving as a result). Since then, a lot have changed. Most high-efficiency toilets are more effective with powerful siphonic action and some are pressure-assisted. Pressure-assisted toilets use the water coming into the tank to pressurize air. The pressurized air is used when flushing, giving extra power to the downward movement of the water during the flush. These are not very common at homes, and more used in commercial situations.
Some toilets sold on amazon.com have a 1.6 gallon flush version and one of 1.28 gallons. The 1.28 gallons versions are generally an adaptation of the 1.6 gallon types. These can be also be shipped to California, Georgia, Texas, and Colorado. If you need a larger flush incidentally you can press and hold the lever or button, effectively leading to emptying of the whole water tank. This is a good backup if the 1.28 gallons flush incidentally is not powerful enough for a good flush.
Calculate water savings by updating to a high-efficiency toilet
Below you can calculate how much water you could save annually by updating your current toilet to a high-efficiency toilet. Just adjust the parameters to your situation.
One example of a high efficiency toilet that has been review on this website is the Toto Ultramax II. This a an elegant one-piece toilet that is a direct successor of the original Ultramax, that used 1.6 gallons per flush.