How Waterless Toilets Work

An advertisement for a composting toilet might simply state, "First it's poop, then it's plant food." And that's pretty much it in a nutshell -- you start with excrement and eventually get fertilizer. So, how do you get started? The first decision is whether to buy or build the toilet. A dozen or more companies sell prefabricated, waterless composting toilets. Home versions can cost anywhere from $850 to as much as $4,000 [source: Ecovita, EcoTech]. A prefabricated toilet usually comes with the assurance of being sanitary. It includes reliable instructions for installation and for tending to the compost.

Do-it-yourself systems can cost as little as $25, if you use a bathroom bucket and outdoor composting heap [source: Jenkins]. Web sites and books rush to tell you how to make one. They don't, however, guarantee that your system won't leak, stink, draw insects or animals, be a health hazard or be illegal. So choose your instructions wisely.

Another decision is choosing between self-contained and remote systems. What you choose depends on your bathroom layout, the number of users and where you want the compost. In a self-contained toilet, the waste composts in your bathroom, inside the toilet. In the Envirolet version, for example, up to six people use it continuously, each tossing in their toilet paper and carbon-rich cover, like peat moss, after each use [source: Envirolet]. The waste breaks down in the toilet. You check it but otherwise leave it for three to six months [source: Envirolet].

In remote systems, the toilet is in your bathroom, but the waste falls down a chute to a composting bin. The bin is in a crawlspace, on the floor below or outside. More people can use these more heavily. For instance, eight people can use Envirolet's remote toilet full-time [source: Envirolet]

During composting, your excrement and the organisms in it are transformed by the temperature, moisture, oxygen, nutrients and bacteria in the compost pile into mature compost, a fertilizer containing microbes different from those that left your digestive tract. Different systems accomplish composting differently. For example, most commercial toilets are set up for slow, low-temperature composting (below 98.6 F or 37 C), which kills most disease-causing organisms in months, giving you fertilizer that's safe for ornamental gardens. For fertilizer that's safe for food-producing gardens, you'd need a high-temperature composting system where the compost cooks at a temperature from 131 F to 140 F (55 C to 60 C) for several hours so that it basically kills all human pathogens [source: Jenkins].

Composting toilets can use power or not. Powered toilets often have fans and heaters that evaporate some urine and aerate the waste to speed composting. The toilets can usually run without power on a plain ventilation pipe. Composting may then be slower, limiting your toilet use by up to half [sources: Envirolet, Envirolet]. Whether it's powered or not, if your toilet composts indoors, you'll need to cut a hole in your roof for the ventilation pipe.

You can also choose whether to separate urine and feces. Usually, they'll drop into the same composting receptacle. But urine-diverting composting toilets have a seat that catches urine. The seat funnels the urine through a pipe that connects to your shower and sink outflow pipes, to a homemade pit or wetland in your backyard, or to a tank, where's it's diluted and can connect to a garden hose. But while you can spray your lawn with diluted urine in Sweden, it's likely against local laws in the United States [source: Ecovita].

Incinerating toilets can also be waterless. Instead of breaking down waste biologically, these toilets torch it. They send the waste to an incinerator, where it's burned to sterile ash.

The toilet sits in your bathroom and has an electric exhaust pipe that exits through your roof. To run, it needs batteries or can be plugged into a wall outlet. You use the toilet normally, toilet paper and all. But before you flush, you must close the lid, for reasons that will soon be clear. Next, you decide whether to press the "urine" or "[solid] waste" button on the control panel.

Then the toilet fires up. Flushing is handled by some type of dry method, like an auger (essentially a large screw) that turns to push the waste into the incinerator. A propane, diesel or natural gas tank feeds into the incinerator. The incinerator injects fuel and ignites your waste, burning it -- in one example, at 800 F (427 C). Urine cooks for up to 10 minutes; solid waste takes about half an hour [source: Ecojohn].

Like composting toilets, these toilets can be self-contained or remote, putting the incinerator either inside or outside of the toilet. Self-contained models have you practically sitting on the incinerator, which sounds alarming, but the system will shut off if you open the lid to use it.

These systems thoroughly insulate you from your excrement. Waste is almost immediately changed into something else. You don't need to inspect the waste, tend to it during its transformation or guess about its progress. It's time to empty the toilet when the indicator light tells you so. In a house of four people, Ecojohn estimates that you'll empty the ashes every three to six months [source: Ecojohn]. And you can throw the sterile ashes in the trash.

An Ecojohn setup costs about $4,000 [source: Propane]. Beyond that, you also pay for propane. Ecojohn says fuel for its toilets costs eight to 10 cents per flush [source: Ecojohn]. Bear in mind, though -- while you conserve water, unless you buy and add a catalytic converter, your incinerator puffs out fossil-fuel fumes [source: Ecojohn].

Read on for some things to consider before installing a waterless toilet.

You should research your toilet before buying it. "Step one is to call the local health department," says Tom Bruursema, general manager of the wastewater treatment unit at the National Sanitation Foundation. Ask whether the toilet you're eyeing meets safety and sanitation standards and whether your planned method of disposing of urine and compost is legal. They'll approve your system based on factors specific to your house, your family, and where you live. The health department can fine you or restrict your use if you install a toilet that's not compliant, says Bruursema.

Beyond trouble with officials, poorly made systems carry risks. The more your system exposes you to untreated or improperly treated human waste, whether during use, cleaning or emptying, the higher your risk for getting sick, says Bruursema. A poorly made system can expose you to pathogenic bacteria, viruses, protozoa and parasitic worms.

If you're wondering about maintenance, it depends on the setup. Composting toilets generally require more work than incinerating toilets or waterless urinals. Basic care is throwing in dry, carbon-rich cover after each use and monitoring the compost. You have to add cover if it's soupy or water if it's too dry.

If you're worried about odors, many commercial toilets build in methods for preventing bathroom stench. For instance, Envirolet toilets use fans to pull air from your bathroom through the toilet and out of a stack on your roof. You seal gaps in the system with silicone [source: Envirolet]. The fans in the toilet aerate the compost and keep the air flowing one-way.

But according to "The Humanure Handbook," written by Joseph Jenkins, who claims to have 30 years of human waste composting experience, all you need to extinguish stench is healthy compost. To achieve that, you must:

If oxygen is smothered, or if liquid or nitrogen build up, that's when things get stinky. But if it's done right, the finished compost will smell like soil.

Waterless toilets must be cleaned like regular toilets. There's no magic here -- just use warm, soapy water to clean the toilet bowl. Some toilets have removable bowls.

Of course, your cleaning does not stop at the toilet bowl. You need to empty the toilet. If it's a composting toilet, emptying times range from months to years, depending on the size and design. Local guidelines may ask you to bury the finished compost, but many times, you can sprinkle it on your garden [source: Envirolet]. To be safe, you can check with your local health department for more information.

Composting toilets, like any toilet, can give you a mess, especially if parts break. But common sense should prevent most messes. If you don't empty the toilet, you'll have obvious problems. Floods are unlikely in most commercial models because they'll have an overflow pipe, so if liquid builds in the composting chamber, it will spout into a pit in your backyard (that you build). A more common backup would be a blockage in your ventilation pipe from leaves, snow or an animal, in which case, you may smell the result.

A discussion of waterless toilets wouldn't feel complete without covering waterless urinals. Men could argue that in emergencies the roadside qualifies as such. But companies do make them -- waterless urinals for the bathroom.

You'll find waterless urinals in crowded public restrooms. Building owners saw that by using dry urinals, they'd save money on water and sewer charges for thousands of flushes. They're installed in the New York Mets Citi Field Stadium and the Shedd Aquarium in Chicago, says Mark Mahoney, a marketing representative for Kohler Co. Waterless urinals are also popping up in states that suffer droughts. Arizona made waterless urinals mandatory in its state buildings in 2005 [source: Sloan].

You can also buy a waterless urinal for your home. Mahoney says his company has sold them for entertainment rooms that he calls "man caves" and to families with several boys. A family with four males, each flushing the 1.5-gallon (5.7-liter) toilet three times a day will save 6,552 gallons (24,802 liters) of water a year by installing and using a waterless urinal [source: ZeroFlush].

Waterless urinals look like regular urinals without a pipe for water intake. Men use them normally, but the urinals don't flush. Instead, they drain by gravity. Their outflow pipes connect to a building's conventional plumbing system. In other words, unlike a composting toilet, which leaves you to deal with your waste, these urinals send the urine to a water treatment plant.

Urinal designs differ by the technology in the drain. For $40, Ecovita sells a plastic basin whose pipe plugs into the wall plumbing [source: Ecovita]. Other companies put a trap (it's a cup) in the drain, which they say stifles urine odors. You fill the trap/cup with water and a proprietary liquid -- usually oil. The liquid simply has to float on the water. The urine sinks, and associated gases can't rise through the oil. A model like this costs from $370 to $600 [source: ZeroFlush, Falcon]. You do have to replace the traps, from every three months to 7,000 flushes, which costs money [source: Falcon, Sloan].

Companies such as Kohler Co. don't use traps but instead put the water and oil in the drain pipe. But trap or none, you periodically clean the urinal by pouring gallons of water down the drain and replacing the proprietary oil, which is neither cheap nor entirely waterless.

For more information, explore company Web sites and temper your do-it-yourself impulse with research on how to build a safe system. Soon, you could be saving water as your neighbors wonder why your garden is blooming so lushly.