Toilets That Conserve Water

Approximately 70 percent of the water flushed down traditional-sized toilets isn't required for effective sewage transport. If a toilet predates 1985, it probably uses between 19 liters and 28 liters (5-7.5 gallons) per flush. The older the toilet, the more water it probably uses. Studies performed in Massachusetts show that in an average 3.2 person household where each person flushes four times a day, the 27 liters (7 gallons) per flush toilet uses 123,770 liters (32,700 gallons) of water a year. Even a 13-liter (3.5-gallon) toilet reduces water use per household to 62,074 liters (16,400 gallons) per year. Studies done at various places around the country show that toilets account for anywhere from 35 to 42 percent of all indoor household water use.

Low-consumption toilets lower building water use by 30 to 40 percent. This reduces the load on municipal sewer systems and saves fresh water supplies. Beginning in 1994, it became illegal to make or sell in the United States any toilet that uses more than 6 liters (1.6 gallons) per flush. These toilets became the center of controversy when the law got ahead of technology, resulting in steep price increases, problems with performance, and unhappy consumers. Once they decided to take a serious look at water consumption levels and water conservation, fixture manufacturers responded with only slight modifications in the basic product design. The flush valve on existing water closets was shut off prematurely, and less water was used with minimum changes to the china fixture. What resulted has contributed more to the negative impressions about 1.6 gpf (gallons per flush) low-consumption toilets than any other factor. Repeated flushing was often necessary to clean the bowl after use.

Even so, two 6-liter flushes still use less water than the former 13 liters (3.4 gallons) per flush, and most times only one flush is actually needed. Over time, manufacturers found ways to increase the swirling effect of the water and clean the bowl better. To achieve low-consumption gravity performance, the size of the trap and other openings were decreased. This resulted in a stronger siphoning action to withdraw the waste, and much improved performance. Still, there was double flushing going on, and modifications continued to be made to enlarge the trapway and water surface areas.

Although no longer legal for new installations in the United States, many older, higher consumption toilets are still in place in existing buildings. Older styles include two-piece, lower pressure models, shallow trap models, and one-piece styles that eliminate the seams between the tank and the toilet. The mechanical systems range from flush-valve commercial toilets to wash down toilets, siphon jets, siphon vortex toilets, and blowout toilets. These styles range between 9.5 liters (2.5 gallons) and 30 liters (8 gallons) per flush. Toilet dams installed in toilet tanks limit the amount of water used in existing toilets.

Watersaver toilets use 6.4 liters to 13.2 liters (1.7-3.5 gallons) of water per flush, which may not be enough of a water savings to meet strict U.S. requirements. They use a conventional flushing action, but save water by employing higher water pressure and better bowl shapes, better methods of filling and emptying, and improved trap configurations.

Some toilets conserve water by offering variable flushing controls. Dual cycle controls allow you to choose how much water you need, as do vertical flush sleeve valves. Pressure-reducing valves save water coming in on supply lines.

There are two types of ultra-low-flow (ULF) toilets currently available to homeowners that meet the legal requirements: the gravity ULF and pressurized ULF. Gravity ULF toilets have steeper-sided bowls to increase the flushing velocity. The tanks are taller and slimmer than older models, raising the water higher and increasing the flushing power. These taller tanks also hold more than 6 liters (1.6 gallons) of water, but the flush valves don't release it all, harnessing only the force of the topmost 1.6 gallons. The tank never empties its entire capacity, and it's a clever way to increase flushing power.

Pressurized ULF toilets look conventional from the outside but use a unique air-assisted flush mechanism inside the tank. The pressure-assist vessel inside the toilet's tank traps air, and as it fills with water, it uses the water supply line to compress the trapped air inside. The compressed air is what forces the water into the bowl, so instead of the pulling or siphon action of a gravity-fed toilet, the pressure-assist unit pushes waste out. This vigorous but somewhat noisy flushing action cleans the bowl better than gravity units.

Pressure-assist flushing systems (Fig. 13-3) reduce water use by elimination of leakage and double flushing. The U.S. Department of Housing and Urban Development (HUD) has calculated that a fixture can leak up to 95 liters (25 gallons) per day, depending on the age of the parts inside, but the pressure-assist unit holds the water within the tank, eliminating leaks. A larger water surface keeps the bowl cleaner, and a larger trap-way and fewer bends eliminate stoppages. Because the water is contained inside the vessel within the tank, condensation doesn't form on the toilet tank. Fewer moving parts reduce maintenance.

Pressure-assist toilets install in the same space as conventional toilets, and require 138 kPa (20 pounds per square inch, psi) of water pressure, which is typical in residential housing. Pressure-assist toilets are used in homes, hotels, dormitories, and light commercial applications, and are available in handicapped accessible

Figure 13-3 Pressure-assist toilet tank.

models. More and more states are mandating the use of pressure technology in commercial structures, primarily to prevent blockages.

In 1986, a severe drought brought the water supplies of San Simeon, California, to a severe crisis level at the same time that the wastewater treatment plant demand was reaching full capacity during the peak use season. The choices were rather grim: new, supplemental water sources, additional waste treatment capacity, or more rationing that would close some of the motel rooms that the city depended on for income. The alternative on which the city finally settled was replacing all toilets with low-consumption pressure assisted types, which reduced water consumption in the town by 39 percent compared to the older 3.5-gpf toilets. As a bonus, bowl stoppages were almost completely eliminated.

With a central compressed-air system, very low water consumption can be achieved. The Microphor flush toilet has a design with two chambers for a flush that uses only 1.4 liters (1.5 quarts) per flush. In the Envirovac system, a vacuum is used to provide a 1.4-liter flush. This system can be used in basements, as the sewer line may run horizontally or even vertically.

Some toilets use a mechanical seal rather than a water trap, and use only about 5 percent of the usual amount of water. Chemical toilets use even less.

An alternative type of toilet is made by Incinolet.

Available as a toilet or a urinal, it has no plumbing connections and reduces waste to a small volume of ash. It requires connection to electric power and a 10-cm (4-in.) diameter vent to the outside.

Composting toilets, sometimes called biological toilets, dry toilets, and waterless toilets contain and control the composting of excrement and toilet paper by aerobic bacteria and fungi. Aerobic digestion generally produces much less odor than anaerobic processes. The composting process transforms the nutrients in human excrement into forms that can be used as a soil conditioner. Composting toilets can be installed where a leaching field or septic tank, with their inherent problems and expenses, are undesirable or impractical, including areas that have placed limits on new septic systems, and in parks and nature sanctuaries.

All composting toilets require a continuous supply of room air drawn into the composting chamber and vented out through the roof to provide oxygen for the aerobic microorganisms that digest the wastes. Composting toilets eliminate or greatly reduce water for flushing but increase energy consumption, although the amount needed to run a fan and keep the compost from freezing is small, and is often supplied by a solar panel on the roof. Grates, screens, electric fans, and ventilation chimneys can provide ventilation. Airtight lids on the toilet, screens over vents, proper maintenance, and keeping kitchen scraps from the composting toilet will deter unwanted insects. Some government agencies require a permit before installing a composting toilet.

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