The toilet isn't just an appliance. It's a privilege. After all, we'd be living in a diseased and disgusting world without these shiny white bowls to accept our bodily waste. Unfortunately, these appliances use a lot of water to do their dirty work. And when drought plagues, we worry that the toilet is flushing away too much of a valuable commodity.

Most people don't realize how much of our water toilets hog. After outdoor irrigation, toilets consume the most water in a residential home. Flushing a toilet accounts for 14 percent of the water used both inside and outside a home [source: Alliance for Water Efficiency]. And if you measure only indoor appliances, the percentage of water used by toilets goes even higher. Flushing a toilet uses 38 percent, or more than a third of the water, utilized indoors in the typical U.S. home [source: Massachusetts Water Resources Authority].

Enter the low-flow or low-flush toilet. Since 1992, U.S. law has mandated that new toilets sold in the United States be low-flow or low-flush, which means that they consume no more than 1.6 gallons (6 liters) per flush. Before that time, typical toilets sold in the United States used 3.5 to 7 gallons (13.24 to 26.5 liters) per flush.

Many people who live in older homes don't have low-flow toilets. But more and more government and nonprofit agencies are urging homeowners to replace those toilets with low-flow models. Many cities and municipal water organizations even offer rebates for purchasing a low-flow toilet.

There are various types of low-flow toilets available, but most use either a gravity or pressure-assisted technology to work. They have varying designs ranging from basic to luxurious. For example, one top-of-the-line low-flow toilet, made by Toto, comes with an optional sound module that can be used to mask bodily noises with everything from the sound of a toilet flushing to the sounds of a running brook or crashing ocean waves.

Sound effects may be a bit over-the-top, but saving water is always a good idea. How do these low-flow toilets get the job done?