Sanitation technology

A ventilated improved pit latrine in Zambia.

Credit: WaterAid / Jon Spaull

Casual defecation "out in the bush" spreads disease. Any latrine, provided it is used, is an improvement on no latrine. In rural situations, family pit latrines can provide satisfactory and acceptable sanitation. They are all that most people in the developing world can afford. Given sensitive guidelines and a little technical help, families can build latrines for themselves, at very low cost.

Simple pit latrines

A family pit latrine should be about 1.2m diameter, or square, (the smallest dimension that can be dug conveniently), with the pit wholly above the water table. It should be at least three metres deep and, if necessary to attain this depth, the floor level of the building above it should be raised above ground level.

With this capacity, the contents of the pit should digest and, in practice, the pit may never become full. By constructing twin pits, it should be possible to dig out a filled pit, after it has stood for a year, without any objectionable smell, whilst the other pit is in use.

Installation of a latrine, Bangladesh.

Credit: WaterAid / Liba Taylor

Concrete cover slabs should not be cast over the pit. Casting the slab in two pieces can reduce the weight to be carried. As an absolute minimum, communities should be supplied with well-designed steel or timber shuttering for the casting of the slabs, and advice on concrete mix proportions.

Well-trained local craftsmen must supervise the mixing and placing of the concrete in the slab.

Pit latrines should be sited at least 50m from the nearest well or borehole. When water is used for anal cleansing this rule can be difficult to enforce and hydrogeological advice should be sought.

A latrine is a permanent installation. In unstable ground the pit walls should be supported with timber, bricks or blocks. Struts spanning across the pit should be avoided as they will become fouled and will cause smells.

The pit cover slab needs to be strong (for obvious reasons) and its top surface should be smooth and easy to keep clean. Concrete is the best material; structural strength can be achieved by a slightly domed shape, or by using steel reinforcement. A superstructure (latrine house) is needed to give privacy and can be built of any local material.

Manuel putting ash and soil down his composting latrine, Mozambique.

Credit: WaterAid / Jon Spaull

Full-scale demonstration latrines, preferably showing the range of designs for squat-holes, should be built in each village before the start of a sanitation project.

It is vitally important that the families should be enabled to provide themselves with what they are happy with, not with what is thought good for them. Each family should be given detailed advice on sitting (preferably downwind, away from trees and not too close to places where food is stored or prepared).

Various modifications of the standard pit latrine are available, depending on local conditions and customs. Sketches of some of these are shown below.

Pour flush latrines

In villages where people use water for anal cleansing, pour flush latrines can be constructed. The squatting slab can then be sited a metre or two away from the pit, to which it drains via a communication pipe. The squatting plate and pit cover are easier to construct and are just as satisfactory.

To prevent smells rising from the pit a U-bend water seal can be incorporated but such seals are worse than useless if they are not properly flushed; a close-fitting squat-hole cover can do the job just as well. Raised "footpads" should be cast into the slab on each side of the squat hole and the surface of the slab should slope towards it.

The ventilated improved pit (VIP) latrine

The ventilated improved pit latrine was introduced in Africa in the 1970s and has proved successful in rural areas in overcoming problems with flies and odours. Its essential features are illustrated in the following diagram:

The interior of the superstructure should be darker than the daylight outside and the superstructure building should be well ventilated so as to allow the flow of air into the pit.

The pit should have a vent pipe which should be at least 100mm diameter and should extend from the pit to about one metre above the roof, and the top of it should be fitted with a fine-mesh stainless steel, GRP or aluminium fly-screen.

Flies which are drawn by smell into the pit will be attracted up the vent pipe by the brightness of daylight at the top it, but cannot escape because of the screen. Wind passing over the vent pipe will cause an updraught, removing any smell and helping to draw flies up to the top of the pipe.

Small scale community sewerage schemes

Rakiya Abdullah shows off her new latrine in Ghana.

Credit: WaterAid / Jon Spaull

In high-density population areas where properties have flushing toilets, it is sometimes possible to install a piped sewerage scheme. Advantages are improved health and a great reduction in smells.

However, disadvantages are the relatively high capital cost, construction difficulties in congested areas and the disposal of the effluent at the end of the system. The topography of the area may well make or break this type of system.

Some schemes of this sort have been very effective where there has been strong community leadership and a real desire in the community to improve conditions.

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References:

Low-Cost Sanitation. John Pickford. IT Publications 1995.

Sanitation without water. Uno Winblad and Wen Kilama. Macmillan Education 1985.

Latrine Building. Bjorn Brandberg. IT Publications 1997.

Sustainable Sewerage. R.A.Reed. IT Publications 1995.