In brief
A toilet without flushing water in which excreta are covered with dry material and slowly turned into a hygienic soil amendment through rotting and storage.
What is a composting toilet?
A composting toilet is a toilet without a flush. What a water closet carries away with several litres of drinking water stays in a container here, is covered with dry, carbon-rich material and then turned, over months, into a soil-like substance. The principle is old. What is new is the knowledge of how to make it hygienic and pleasant, gathered over the past decades by sanitation research, especially in Scandinavia and in development cooperation.
Excreta on their own are too wet and too rich in nitrogen to compost well. Faeces have a carbon to nitrogen ratio of only around 7 to 8, while microbes work best at 25 to 30. The cover material, usually sawdust, wood shavings, dry leaves or chopped straw, closes this gap. It absorbs moisture, binds smells, keeps flies away and supplies the carbon. Without it there is no rotting, only a wet, smelly mass.
Designs: urine diversion, composting chambers and the bucket system
Urine-diverting dry toilets have a seat or pan with two openings or zones: urine flows forward into a container or soak pit, faeces fall behind into a chamber. Covered with ash, sawdust or soil, the faeces dry out rather than compost in the strict sense. Many of these toilets have two chambers used in turn: while one fills, the other rests and dries.
Composting chambers keep the material moist enough for real composting, often together with kitchen scraps. A vent pipe draws air through the chamber. In continuous systems the fresh material enters at the top and finished compost is taken out at the bottom; in batch systems a chamber is filled, closed and left to mature while a second one is in use. Batch systems are considered safer, because fresh and mature material never mix.
The bucket system is the simplest form, described in detail by Joseph Jenkins in The Humanure Handbook. A bucket under a seat is filled with a little cover material after each use. When full, it is emptied into a dedicated compost bin outdoors, covered with straw or leaves, and composted hot together with garden and kitchen waste. Jenkins works with two bins: one is filled for about a year, then rests for about a year while the second is filled. The real treatment happens in this second stage.
Rotting, storage time and hygiene
Human faeces can carry pathogens: bacteria, viruses, protozoa and the eggs of parasitic worms. The WHO guidelines on the use of excreta in agriculture therefore set out clear barriers. A thermophilic compost should reach and hold at least 50 degrees Celsius for at least a week; because a heap rarely heats evenly throughout, a longer composting period is needed in practice. Where there is no heat, storage time takes over: one and a half to two years at 2 to 20 degrees, more than a year above 20 degrees. If ash or lime raise the pH above 9, the period shortens to at least six months. The eggs of the roundworm Ascaris are the most persistent and determine these times.
Further barriers follow from the same guidelines. Even treated material is worked into the soil rather than spread over leaves, and at least a month passes between the last application and the harvest. Crops eaten raw are where most care is needed; fruit trees and ornamental plantings are the safest destination.
Urine as a nitrogen fertiliser
Urine contains most of the nutrients a person excretes. In the example values from Sweden used by the Stockholm Environment Institute, an adult excretes around 550 litres of urine a year, holding about 4 kilograms of nitrogen and 0.37 kilograms of phosphorus, compared with about 0.55 kilograms of nitrogen and 0.18 kilograms of phosphorus in faeces. Urine therefore carries close to nine tenths of the nitrogen and about two thirds of the phosphorus. The figures vary with diet.
Fresh urine from healthy people contains few pathogens; the main risk is contamination with faeces. For a household that uses its own urine on its own crops, the WHO guidelines allow direct use, with a month between fertilising and harvest. Where crops are eaten by others, they recommend storing it for at least six months at 20 degrees or more. Urine is often diluted with about three parts water, applied around the plants and worked in quickly. It also carries salt. Where little rain falls to wash the soil through, it makes sense to change the spot from time to time and keep doses moderate.
Closing the loop between kitchen, people and soil
The nutrient cycle of a farm breaks at one point more completely than at any other: what the harvest carried away passes through people and ends up in the sewer. The composting toilet closes this gap. Food comes from the soil, passes through kitchen and body, and returns as compost and urine fertiliser to the place it came from.
It saves water as well. In homes in the United States toilets account for close to 30 percent of indoor water use, according to the EPA. On dry land without a sewer, where greywater from washing is already being returned to the garden, the composting toilet takes the second step: no drinking water is used to carry nutrients away.
Frequently asked
What is a composting toilet?
A composting toilet is a toilet that works without flushing water. Instead of being washed away, faeces are covered after each use with a dry, carbon-rich material such as sawdust, wood shavings or dry leaves. This binds moisture and smells and gives the microbes the carbon they need. The material is then rotted and stored, in a chamber below the toilet or in a separate compost bin, until it has become a soil-like substance. Many designs collect urine separately, because it is a valuable fertiliser on its own and makes the solid part much easier to handle.
Does a composting toilet smell?
A well run one does not, or hardly. Smell arises mainly where urine and faeces mix and stay wet, so that ammonia escapes and the material begins to rot without air. Enough cover material after each use solves most of this: it absorbs liquid and forms a dry layer on top. Urine diversion helps further, as does a vent pipe that draws air out of the chamber. When a composting toilet smells, the cause is usually too little cover material, too much moisture, or a vent that does not draw.
Is humanure compost safe?
It can be, if time and temperature are allowed to do their work. The WHO guidelines on the use of excreta in agriculture name two routes. A hot compost should reach at least 50 degrees Celsius for at least a week, which in practice takes a longer composting period. Without heat, storage does the job: one and a half to two years at 2 to 20 degrees, over a year above 20 degrees, and shorter when ash or lime raise the pH above 9. The eggs of the roundworm Ascaris are the most persistent pathogen and set the pace.
How do you use urine as fertiliser?
Urine is a fast-acting nitrogen fertiliser. In household practice it is often diluted with about three parts water and poured onto the soil around plants, not onto leaves, and worked in or watered in quickly so that less nitrogen escapes as ammonia. It suits hungry crops during their main growth; fertilising stops about two thirds to three quarters of the way to harvest, and the WHO guidelines leave at least a month between the last application and the harvest. One person's urine for a year is enough for roughly 300 to 400 square metres of crops, according to the Stockholm Environment Institute.
How much water does a composting toilet save?
All of the water that would otherwise be flushed. In homes in the United States, toilets account for close to 30 percent of indoor water use, according to the US Environmental Protection Agency. In a dry region that is drinking water used to transport a few hundred grams of material. The composting toilet also keeps nutrients out of wastewater, where they would cause pollution, and returns them to the land. It needs no sewer connection, which makes it especially interesting for remote sites, gardens and land without a mains supply.
Related terms
Mentioned in
Permaculture principles at work here
The design principles after David Holmgren that this page puts into practice.
Sources
- WHO, Guidelines for the safe use of wastewater, excreta and greywater, Volume 4: Excreta and greywater use in agriculture, Tables 4.4 to 4.6, pp. 68-70 (2006)
- Jönsson, Richert Stintzing, Vinnerås and Salomon, Guidelines on the Use of Urine and Faeces in Crop Production, EcoSanRes Publications Series 2004-2, Stockholm Environment Institute, Table 1 and p. 7 (2004)
- Schönning and Stenström, Guidelines for the Safe Use of Urine and Faeces in Ecological Sanitation Systems, EcoSanRes Publications Series 2004-1, Stockholm Environment Institute, Table 1 and p. 7 (2004)
- Tilley, Ulrich, Lüthi, Reymond, Schertenleib and Zurbrügg, Compendium of Sanitation Systems and Technologies, 2nd revised edition, Eawag (2014)
- Joseph Jenkins, The Humanure Handbook, 4th edition (2019)
- US EPA WaterSense, Residential Toilets (online, accessed 2026)
Last updated: 2026-10-15