How Low Can You Flow? How to Create an Energy-Efficient Bathroom

1 / 8
The McDry urinal from Duravit uses oil to trap and seal urine—without water.
2 / 8
Toilets from Toto of Japan are among brands highly regarded for non-clogging low-flushing.
3 / 8
4 / 8
The Caroma Caravelle dual-flush toilet: Press one button to flush urine, another to flush feces.
5 / 8
A specially engineered planter in one bedroom uses graywater from the adjacent bathroom’s bathtub.
6 / 8
The TOTO Zoe Washlet is a high-performing low-flush toilet with built in bidet and air dryer.
7 / 8
8 / 8
In Diane Cotman’s house in Cambridge, Massachusetts, a SeaLand Traveler one-pint flush toilet drains to an EcoTech Carousel composting toilet system below. The home’s hot water is heated by a geothermal heat pump and a solar hot water heater.

Every day, water and heat disappear down the drain in your bathroom, making this room the first place to look for cutting costs and resource use. Starting with faucet aerators, low-flow showerheads, and low-flush toilets, a plan for resource efficiency in bathrooms might also include composting toilets, micro-flush toilets, dual-flush toilets, and even systems irrigated with graywater.

For a look at just how far you can go–should you have the desire and the means–step inside Diane Cotman’s turn-of-the-century home in Cambridge, Massachusetts. In one bathroom, a trim white SeaLand Traveler toilet flushes with just one pint of water via a foot-pedal on the side. The toilet drains to an EcoTech Carousel composting toilet system in the basement that processes the waste into a soil-like humus. In another bathroom, a high-tech and high-design Toto Zoe Washlet toilet provides non-clogging 1.6-gallon-flushing–as well as a built-in bidet, air dryer, and deodorizer. A stainless steel bathtub recirculates hot water through the walls of the tub, keeping bathwater warm.

Wastewater from Cotman’s sinks and tubs–called “graywater”–is filtered and drained to specially engineered planters in window alcoves in the bedrooms, where it is used to water plants such as orchids, birds of paradise, and other colorful tropical varieties. Solar collectors and a geothermal pump heat the water for the house’s sinks and tubs as well as the radiant heating and cooling system.

Cotman’s bathrooms are an extreme example, but there’s plenty to do for those seeking simpler solutions.


A 1.6-gallon low-flush toilet can cut household water usage by 20 percent or more. Required in all new construction, low-flush toilets have come a long way since the early days, when most U.S. low-flush models were prone to double-flushing and clogging. Changes in design have produced high-performing units that can significantly reduce home water use and take a load off septic systems and municipal water supplies.

Every low-flush toilet conserves between twenty-five and sixty gallons of water per day each, saving owners an estimated $50 to $100 on annual water bills.

Recognizing that less water is needed to flush urine, new “dual-flush” toilets feature two flush buttons: Press the dark one to flush feces with 1.6 gallons of water or press the light one to flush only urine with 0.8 gallon. Caroma’s dual-flush from Australia (where this style is mandated for all new buildings) is now imported to the United States; prices start at $250.

Waterless urinals are another easy water-saving solution. These feature seals that allow urine to drain without water or odors. Prices start at $350.

Composting toilets, which biologically process excreta, are usually chosen by property owners with environmentally sensitive sites or limited water. Generally, there are two types. Self-contained units, in which the toilet seat and the composter are one unit, sit on the floor and are generally best for occasional use, such as in cottages or cabins. Under-floor or “central” units feature a toilet stool in the bathroom that drains to a large-capacity composter underneath. Composting toilets are used with one-pint-flush, foam-flush, urine-diverting toilets, as well as dry toilet stools. In many states, they allow owners to reduce the size of their septic drainfields. Prices range from $770 for a self-contained model to $4,500 for an under-floor model.

Showerheads and faucet aerators

Showerheads and faucet aerators pressurize tap water flow and mix it with air to produce a stream that quickly wets and rinses but uses about 70 percent less water. These attach to the tap end of faucets and can reduce flow to as little as 0.5 gallons per minute (gpm).

A showerhead rated at 1.8 gpm at 50 psi (nearly half the national standard) can give a satisfying water-saving shower. Choose one with a shut-off valve so you turn off the flow while soaping up. Try several at the same flow rate to find one you like, and return the rest.

A Rainshow’r chlorine-filtering low-flow showerhead ($49) will also protect skin from drying chlorine.

On-demand water heaters

Gallons of water run down the drain while we wait for hot water–often two to three gallons per shower. Multiply that by the number of people in your household, and that can add up to thousands of gallons per year.

Increasingly, builders are placing water heaters closer to where they’re needed so warm water is available immediately and heat is not lost along the way. Consider installing small five- to ten-gallon hot water heaters closer to bathrooms.

On-demand or “tankless” hot water heaters, commonly used in other countries, heat water when and where it’s needed for an endless supply. Prices for a small system start at $180.

Or, capture the heat of the hot water as it runs down the drain. Hot water recirculators ($1,000 installed) constantly circulate hot water through pipes from the heater to the farthest fixture, so the water is always hot, and no water is wasted waiting for the flow to warm up. (Be sure to insulate pipes and consider adding a timer, so circulation starts only during showers.)

Graywater heat exchang-ers, such as those by GFX Technology (starting at $200), capture the heat of washwater before it leaves the house and transfer it back to the water heaters or fixtures.


Keep the air in your bath fresh with a ventilation fan. Mary Cordaro, of H3 Environmental in Valley Village, California, suggests running an exhaust fan during a bath or a shower and keeping it on for thirty minutes afterward to dehumidify the room. The best models combine energy efficiency with quiet fans. The Panasonic WhisperFit and Super-Quiet exhaust ceiling fans are the best choices for low sone (noise level) and low wattage, which save energy and are quiet enough for that long, contemplative soak. $105 to $128 in the Green Builders Catalog: (800) 488-4340, or from Panasonic: (866) 888-2929.