Pit latrine

Interior of an outhouse the structure usually built over the pit to provide privacy

A pit toilet or pit latrine is a type of toilet that does not need water for flushing. It collects human feces (faeces) in a hole underground and infiltrates any liquids, primarily urine, into the ground. It is the least expensive method of separating feces from people even though this separation is not always complete. When properly built and maintained (maintenance becomes an issue when the pit is full) they can decrease the spread of disease by reducing the amount of human excreta in the environment and therefore reducing flies from transferring bacteria, viruses, and parasites between feces and food. Not using toilets, or open defecation, is believed to result in the death of more than 0.75 million children a year and 250 million lost school days from diarrhea.

A pit toilet is made up of five parts: a hole in the ground, a base, a floor with a hole in it, a mound around the floor, and a building on top. The World Health Organization recommends that they are built about 6 meters (6.6 yards) from the house, at least 30 meters (32.8 yards) from water sources, and at least 2 meters (2.2 yards) above the water table when it is at its highest. When the pit fills to within 0.5 meters of the top, it should be emptied or a new hole dug and the superstructure moved. If the pit is to be emptied by hand, two years must pass after last usage before this can be considered safe enough although strict hygiene procedures (gloves, boots, etc.) must be followed in any case during pit emptying. The size of the hole in the floor should not be larger than 25 centimeters (9.8 inches) to prevent children falling in. Light should be prevented from entering the pit to reduce access by flies. This requires the use of a lid to cover the hole in the floor when not in use.

A basic pit toilet can be improved in a number of ways. One includes by adding a ventilation pipe from the pit to above the structure. This improves airflow and decreases the smell of the toilet. It also can reduce flies when the top of the pipe is covered with mesh (usually made out of fiberglass). In these types of toilets a lid need not be used to cover the hole in the floor. Other possible improvements include a floor constructed so fluid drains into the hole and a reinforcement of the pit to prevent its collapse. Ashes or sawdust can also be added on top of the feces to decrease the smell.

As of 2013 pit toilets are used by an estimated 1.77 billion people. This is mostly in the developing world as well as in rural and wilderness areas. In 2011 about 2.5 billion people did not have access to a proper toilet and one billion defecate outside. Southern Asia and Sub-Saharan Africa have the poorest access to toilets. In the developing world the cost of a simple pit toilet is between 25 and 60 USD. In India the "No Toilet, No Bride" slogan is used successfully to promote toilets by encouraging women to refuse to marry a man who does not own a toilet.

Pit

Digging the pit for a pit toilet in Cap-Haitien, Haiti.

A night soil man, known in his country as a frogman, manually removing the waste from a permanent concrete-lined pit toilet in Dar es Salaam, Tanzania.

Some pit toilets, which are used by a great number of people—such as a public restroom in rural areas, or in a woodland park or busy lay-by, rest stop or other similarly busy location—are built with a concrete lining for permanence. In this type, the pit is periodically emptied, usually by a pump mounted on a large truck which also carries a tank for storage. The waste is transported by road to a sewage treatment facility, or to be composted elsewhere. There are numerous licensed waste hauling companies providing such service in areas where it is needed.

In Dar es Salaam, Tanzania, where most human excrement is thrown into alleys or gulleys, pit latrines costing up to $300 are 10 ft (3.0 m) deep and lined with concrete slabs, while cheaper “temporary toilets” consist of a pits lined with two stacked oil drums or a stack of tires. These latrines, which are often used by several households, may be emptied by vacuum truck, manual digging, or overflowing into streets during rains.

Dry pit

This concrete-lined waste pit is one type of dry pit design. A dry pit does not penetrate the water table, while a wet pit does. In locations near streams or where undue seepage may occur, such as on a slope, the dry pit design may be preferred, even with low traffic use.

Types

The slit-trench latrine is the simplest type of pit toilet, consisting of a relatively shallow (3–6 feet/1–2 metres in depth) trench narrow enough to stand with one leg on either side. This type is used either by squatting, with the users' legs straddling the pit, or by various arrangements for sitting or leaning against a support structure. Such support may vary from the simplest forms such as a log, plank, branch or similar arrangement placed at right angles to the long axis of the pit.

A cathole is a one-time use pit toilet often utilized by campers, hikers and other outdoor recreationalists.

Advanced designs

A vacuum tanker for pit emptying in Chiang Mai, Thailand.

An advanced pit toilet is more complex forms, or higher capacity forms - commonly associated with outhouses though sometimes used underneath a house, or as a central collection area for several outhouses or other waste collection arrangements - the pit will be larger, and covered with a supporting structure. This structure may be simply a metal plate, or board floor - with a hole over which the user positions themselves during use. A provision for seating is often placed above a pit toilet, this may be a simple hole, or several holes, in a board surface at sitting height. In bitter cold Arctic climates, honey buckets are used inside the home and carried to such covered pits outside.

A more substantial structure may also be built. Commonly known as an outhouse, these small enclosed buildings provide a roof for shelter, one or more seats with a hole in it, and occasionally access to water for washing.

Ventilated improved pit (VIP)

The ventilated improved pit latrine (VIP), is a pit toilet with a black pipe (vent pipe) fitted to the pit, and a screen (flyscreen) at the top outlet of the pipe. VIP latrines are an improvement to overcome the disadvantages of simple pit latrines, i.e. fly and mosquito nuisance and unpleasant odors. The smell is carried upwards by the chimney effect and flies are prevented from leaving the pit and spreading disease.

The principal mechanism of ventilation in VIP latrines is the action of wind blowing across the top of the vent pipe. The wind creates a strong circulation of air through the superstructure, down through the squat hole, across the pit and up and out of the vent pipe. Unpleasant faecal odors from the pit contents are thus sucked up and exhausted out of vent pipe, leaving the superstructure odor-free. In some cases solar-powered fans are added giving a constant outwards flow from the vent pipe.

Flies, searching for an egg-laying site are attracted by faecal odors coming from the vent pipe, but they are prevented from entering by the flyscreen at the outlet of the vent pipe. Some flies may enter into the pit via the squat hole and lay their eggs there. When new adult flies emerge they instinctively fly towards light. However, if the latrine is dark inside the only light they can see is at the top of the vent pipe. Since the vent pipe is provided with a fly screen at the top, flies will not be able to escape and eventually they will die and fall back into the pit.

To ensure that there is a flow of air through the latrine there must be adequate ventilation of the superstructure. This is usually achieved by leaving openings above and below the door, or by constructing a spiral wall without a door.

Absorbents

Covering the feces with an absorbent decreases smell and discourages flies. These may include soil, sawdust, ash or lime among others. In developing countries, the use of absorbents in pit toilets is not commonly practiced.

Limitations of pit toilets

Pit latrines are often built in developing countries even in situations where they are not recommended. These include:

• Frequent flooding, resulting in inoperable toilet systems and the contamination of water resources;
• Unfavourable soil conditions, such as unstable or rocky soil and high water table, making pit-based sanitation difficult and expensive;
• When groundwater is the primary source of drinking water and is likely to be contaminated by pit-based sanitation (for example in denser settlements or with unfavourable hydrogeological conditions);
• Limited land space restricts the excavation of new pits if full pit latrines are usually not emptied;
• Indoor installations are preferred as they provide greater comfort and security at night thus making them more accessible for all

Further reading

• Types of toilet and their suitability Practical Action
• Single pit latrine Akvopedia