What is it? Pit latrine designs range from simple unimproved pit latrines, through Ventilated Improved Pit latrines (VIPs) to alternating twin pit systems. In a twin pit system, the second pit is only used when the first pit is filled. The first pit is left sealed for a year or more before emptying during which time disease-causing organisms are destroyed by natural processes. After such storage, without the addition of fresh wastes, the contents become safe to handle, and may be used as compost.
The basic components of a pit latrine are the pit, ideally 4-5 meters deep, a cover slab with a hole through which users defecate into the pit and a superstructure, sufficient to ensure privacy and provide protection from the weather. It must be possible to clean the slab. Partly for this reason, most slabs are made of concrete but it is possible to use a smaller concrete or plastic ‘SanPlat’ laid on top of a latrine cover made from wood and other ‘natural’ materials. VIPs are pit latrines incorporating a vent pipe, designed to draw flies and smells away from the pit and cabin. The flies are trapped by a screen located at the top of the vent pipe and eventually die.
When to use it? Pit latrines are the best conventional sanitation option when there is no source of water on or close to the plot so that water use is low (typically less than 25 liters per person per day). They may also be used when water consumption is higher, provided that separate provision is made for sullage (“gray” water) disposal. However, they may be less attractive to users of pour-flush toilets in such situations.
Advantages: Simple pit latrines and SanPlat systems are cheap. VIPs and twin pit designs are more expensive but still cheaper than other sanitation options.
Disadvantages: Simple unimproved pit latrines may smell. VIPs should be better but users may not appreciate the need for a dark interior and may modify the superstructure to provide more light, thus undermining the basic rationale behind the design. The VIP design is very dependent on a durable fly screen and may give rise to insect problems if the screen fails for any reason. Emptying the pits may be problematic, and people may opt to dig a new pit and move the superstructure into a new location, if land is available. High water table and/or flooding are obvious problems for pit latrines.
Technical requirements: The slab must be structurally sound and easy to clean. Where vents are adopted, they should extend well above the roof of the latrine superstructure, as this will ensure a good draft of air up the pipe. The vent screen must be made of a corrosion-resistant material. Access to the pit to remove the contents may be via slabs outside the superstructure. Alternatively, a hole can be provided in the wall through which a tanker suction pipe can be introduced. This arrangement is more likely to be effective if the pit contents are wet.