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:
Bucket toilet – a very basic type of dry toilet consisting only of a bucket which could be upgraded with urine diversion and the use of covering material
Simple pit latrines: those pit latrines that do not have a water seal.
Incinerating toilets, freezing toilets – these are toilets with more complicated technology and higher costs
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.
Terminology
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 into the same pit. Some publications use the term "dry sanitation" to denote a system that includes 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". 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.
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Uses
Dry toilets 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 are also used in rural areas of developed countries, e.g. many Scandinavian countries for summer houses and in national parks.
Advantages
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:
To save water – when there is either water scarcity, water is costly or because the user wants to save water for environmental reasons. However, water savings from dry toilets might be insignificant compared to other possible water savings in households or within agricultural practices.
To enable safe reuse of excreta, after the collected excreta or fecal sludge has undergone further treatment for example by drying or composting.
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.
Challenges
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 tend to make it very difficult to empty the pit in a safe manner when they are full. On the other hand, dry toilets that are not connected to a pit usually have a safe method for emptying built into them as they are designed to be emptied on a regular and quite frequent basis.
Urban settings
The use of dry toilets in urban settings of developed countries is very rare as they come with some significant social and technical challenges. Legal acceptability and support at the local policy level amongst the various government departments involved might be very low for dry toilets.
History
The history of dry toilets is essentially the same as the history of toilets in general as well as the history of ecological sanitation systems with regards to reuse of excreta in agriculture.
Dry earth closets
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 Stinkin the summer of 1858, he invented what he called the 'dry earth system'. In partnership with James Bannehr, he patented his device. Among his works bearing on the subject were The Advantages of the Dry Earth System , The Impossibility overcome: or the Inoffensive, Safe, and Economical Disposal of the Refuse of Towns and Villages, The Dry Earth System, Town Refuse, the Remedy for Local Taxation, and National Health and Wealth promoted by the general adoption of the Dry Earth System''. 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.
Great Britain
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.
Australia
, Australia was largely unsewered until the early 1970s, with many suburbs having a dry toilet 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".
