Drainage standard 1: Drainage work
People have an environment in which health risks and other risks posed by water erosion and standing water, including stormwater, floodwater, domestic wastewater and wastewater from medical facilities, are minimised.
- Provide appropriate drainage facilities so that dwelling areas and water distribution points are kept free of standing wastewater and that stormwater drains are kept clear (see guidance notes 1–2, 4–5).
- Seek an agreement with the affected population on how to deal with the drainage problem and provide sufficient numbers of appropriate tools for small drainage works and maintenance where necessary (see guidance note 4).
- Ensure that all water points and hand washing facilities have effective drainage to prevent muddy conditions (see guidance note 2).
Key indicators(to be read in conjunction with the guidance notes)
- Water point drainage is well planned, built and maintained. This includes drainage from washing and bathing areas as well as water collection points and hand washing facilities (see guidance notes 2 and 4).
- There is no pollution of surface water and/or groundwater sources from drainage water (see guidance note 5).
- Shelters, paths and water and sanitation facilities are not flooded or eroded by water (see guidance notes 2–4).
- There is no erosion caused by drainage water (see guidance note 5).
- Site selection and planning: The most effective way to control drainage problems is in the choice of site and the layout of the settlement (see Shelter and settlement standards 1–2).
- Wastewater: Sullage or domestic wastewater is classified as sewage when mixed with human excreta. Unless the settlement is sited where there is an existing sewerage system, domestic wastewater should not be allowed to mix with human excreta. Sewage is difficult and more expensive to treat than domestic wastewater. At water points and washing and bathing areas, the creation of small gardens to utilise wastewater should be encouraged where possible. Special attention needs to be paid to prevent wastewater from washing and bathing areas contaminating water sources.
- Drainage and excreta disposal: Special care is needed to protect toilets and sewers from flooding in order to avoid structural damage and leakage.
- Promotion: It is essential to involve the affected population in providing smallscale drainage works as they often have good knowledge of the natural flow of drainage water and of where channels should be. Also, if they understand the health and physical risks involved and have assisted in the construction of the drainage system, they are more likely to maintain it (see Vector control section). Technical support and tools may then be needed.
- On-site disposal: Where possible, and if favourable soil conditions exist, drainage from water points, washing areas and hand washing points should be on-site rather than via open channels, which are difficult to maintain and often clog. Simple and cheap techniques such as soak pits or the planting of banana trees can be used for on-site disposal of wastewater. Where off-site disposal is the only possibility, channels are preferable to pipes. Channels should be designed both to provide flow velocity for dry-weather sullage and to carry stormwater. Where the slope is more than 5 per cent, engineering techniques must be applied to prevent excessive erosion. Drainage of residuals from any water treatment processes should be carefully controlled so that people cannot use such water and it does not contaminate surface or groundwater sources.