A dry toilet (or non-flush toilet, no flush toilet or toilet without a flush) is a toilet that operates without flush water, unlike a flush toilet. The dry toilet may have a raised pedestal on which the user can sit, or a squat pan over which the user squats in the case of a squat toilet. In both cases, the excreta (both urine and feces) falls through a drop hole. The urine and feces can either become mixed at the point of dropping or stay separated, which is called urine diversion. Dry toilets do not produce sewage. Many types of toilets without a water seal (also called dry toilets or "non-flush toilets") exist. These types of toilets do not use water as an odor seal or to move excreta along. For example, from simple to more complex: a bucket toilet (honey bucket), a tree bog or arborloo (two simple systems for converting excrement to direct fertiliser for trees), a pit latrine (a deep hole in the ground; but not those that operate on a "pour flush" basis), a vault toilet (which keeps all the waste underground until it is pumped out), a container-based toilet, a composting toilet (which mixes excreta with carbon-rich materials for faster decomposition), a urine-diverting dry toilet (which keeps urine separate from feces), and incinerating and freezing toilets.
There are several types of toilets which are referred to as "dry toilets". All of them work without flush water and without a connection to a sewer system or septic tank:
Other types of dry toilets are under development at universities, for example since 2012 funded by the Bill and Melinda Gates Foundation. Such toilets are meant to operate off-the-grid without connections to water, sewer, or electrical lines.
One important source states that the term "dry toilet" should only refer to the "user interface" and not the subsequent storage and treatment steps. However, in the WASH sector, the term "dry toilet" is still used differently by different people. It often includes also the storage and treatment steps. For example, it is common that the term "dry toilet" is used to refer specifically to a urine-diverting dry toilet or a composting toilet.
People also use the term to refer to a pit latrine without a water seal even though the pit of a pit latrine is not usually dry. The pit can become very wet because urine mixes with feces in the pit and drainage might be limited. Also, groundwater or surface water can also get into the pit in the event of heavy rains or flooding. Sometimes households even discard greywater (from showering) into the same pit.
Some publications use the term "dry sanitation" to denote a system that includes dry toilets (in particular urine-diverting dry toilets) connected to a system to manage the excreta. However, this term is not in widespread use nowadays, and might rather be replaced with "non sewer-based sanitation" or "non-sewered sanitation" (see also fecal sludge management).
The term "outhouse" refers to a small structure, separate from a main building, which covers a pit toilet or a dry toilet. Although it strictly refers only to the structure above the toilet, it is often used to denote the entire toilet structure, i.e. including the hole in the ground in the case of a pit latrine.
Dry toilets (in particular simple pit latrines) are used in developing countries in situations in which flush toilets connected to septic tanks or sewer systems are not possible or not desired, for example due to costs. Sewerage infrastructure costs can be very high in instances of unfavorable terrain or sprawling settlement patterns.
Dry toilets (in particular composting toilets) are also used in rural areas of developed countries, e.g. many Scandinavian countries (Sweden, Finland, Norway) for summer houses and in national parks.
Dry toilets can be a suitable alternative to water-flushed toilets when water for flushing is of short supply. Another reason for using dry toilets can be that the infrastructure to deal with the wastewater produced from flush toilets is too expensive to construct.
Dry toilets are used for three main reasons instead of flush toilets:
Dry toilets and excreta management without sewers can offer more flexibility in construction than flush toilet and sewer-based systems. It can be a suitable system to adapt to climate change scenarios in desert-like areas like Lima, Peru.
Dry toilets do not have a water seal, thus odors may be a problem. This is often the case for pit latrines, UDDTs or composting toilets if they are not designed well or not used properly.
Dry toilets that are connected to a pit (such as pit latrines) tend to make it very difficult to empty the pit in a safe manner when they are full (see fecal sludge management). On the other hand, dry toilets that are not connected to a pit (e.g. container-based toilets, UDDTs and composting toilets) usually have a safe method for emptying built into them as they are designed to be emptied on a regular and quite frequent basis (within days, weeks or months).
Further information: Toilet § History
The history of dry toilets is essentially the same as the history of toilets in general (until the advent of flush toilets) as well as the history of ecological sanitation systems with regards to reuse of excreta in agriculture.
Dry earth closets were invented by English clergyman Henry Moule, who dedicated his life to improving public sanitation after witnessing the cholera epidemics of 1849 and 1854. Impressed by the insalubrity of the houses, especially during the Great Stink in the summer of 1858, he invented what he called the 'dry earth system'.
In partnership with James Bannehr, he patented his device (No. 1316, dated 28 May 1860). Among his works bearing on the subject were The Advantages of the Dry Earth System (1868), The Impossibility overcome: or the Inoffensive, Safe, and Economical Disposal of the Refuse of Towns and Villages (1870), The Dry Earth System (1871), Town Refuse, the Remedy for Local Taxation (1872), and National Health and Wealth promoted by the general adoption of the Dry Earth System (1873). His system was adopted in private houses, in rural districts, in military camps, in many hospitals, and extensively in the British Raj. Ultimately, however, it failed to gain public support as attention turned to the water-flushed toilet connected to a sewer system.
In Germany, a dry toilet with a peat dispenser was marketed until after the Second World War. It was called "Metroclo" and was manufactured by Gefinal, Berlin.
In Britain, use of dry toilets continued in some areas, often urban areas, through to the 1940s. It seems that these were often emptied directly onto their gardens, where the excreta was used as fertilizer. Sewer systems did not come to some rural areas in Britain until the 1950s or even after that.
Brisbane, Australia was largely unsewered until the early 1970s, with many suburbs having a dry toilet (called a dunny) behind each house. Academic George Seddon claimed that "the typical Australian back yard in the cities and country towns" had, throughout the first half of the twentieth century, "a dunny against the back fence, so that the pan could be collected from the dunny lane through a trap-door".