Individiual Housing level Water Supplies
Introduction | Individual Housing level | Neighborhood level | Village/Community level | References
Rain water harvesting on the individual housing scale

Falling rain can provide some of the cleanest naturally occurring water that is available.  This is result of a natural distillation process that is at risk only from airborne particles and from man-made pollution caused by the smoke and ash of fires and industrial processes, particularly those which burn fossil fuels.

The term “rainwater harvesting” is usually taken to mean “the immediate collection of rainwater running off surfaces upon which it has fallen directly”. This definition excludes run-off from land watersheds into streams, rivers, lakes, etc.
Rain water collection Barrels
Materials
  • Clean Barrel, Preferably Plastic barrel with a secure lid, Clay pottery, concrete catchments structures also acceptable. Secure lids are important to avoid algae growth and contamination.
  • Galvanized corrugated Iron, aluminum or asbestos cement sheets, tiles slates, thatched roofs tied with bamboo gutters laid in proper slopes. Avoid painted roofs due to chemical contamination.
  • Filter screen to filter small debris and animal droppings
  • Hand or motorized pump to retrieve water.
  • overflow water hose in the event water capacity of barrel is met.
  • filter funnel to divert initial contaminated waters
  • ext.

 

Roofing

Rainwater can be collected from most forms of roofs.  Tiled roofs, or roofs sheeted  with  corrugated mild steel etc., are preferable, since  they are the easiest to use and give the cleanest water.  Thatched or palm leafed surfaces are  also feasible, although they are difficult to clean and can often taint the run-off.  Asbestos sheeting or lead-painted surfaces should be avoided.

Filter Systems

The guttering drains to a down-pipe which  discharges into a storage tank.  The down-pipe should be made to swivel so that the collection of the first run-off can be run to waste (the first foul flush), thus preventing accumulated bird droppings, leaves, twigs and other vegetable matter, as well as dust and debris, from entering the storage tank.  Sometimes a collecting box with a mesh strainer (and sometimes with additional filter media) is  used to prevent the ingress of potential pollutants. 
Optional Foul-Flush Box

The run-off from a roof is directly proportional to the quantity of rainfall and the plan area of the roof.   For every 1mm of rain a square metre of roof area will yield 1 litre of water, less evaporation, spillage losses and wind effects.  The guttering and downpipes should be sized so as to be capable of carrying peak volume of run-off;  in the tropics this can occur during high intensity storms of short duration.

  

Storage

The capacity of the storage tank is based upon several design criteria:  rainfall patterns and volume, the duration of the dry period and, of course, the estimate of demand. Sometimes sophisticated calculations are involved, but these tend not to take into account human behaviour and the willingness to use water if it is available and not to conserve it for future use, in the hope that the dry spell will soon be over.

The provision of the storage tank is the most costly element of a rainwater harvesting project, usually about 90% of the total cost.   Storage can range from small containers made for other purposes, for example oil drums, food cans, etc., but used as domestic storage, up to large tanks of 150 cu.  metres or more at ground level, or sometimes beneath it;  these are made of concrete or ferrocement and are used as storage for schools, clinics or other institutions with large areas of roof.

 

Maintenance
  • It is important to clean out water catchments barrels once a year.
  • It is important not to disturb water, this will create sediments to re-circulate in water
  • remove and clean filter mesh of debris and sediment
  • clean gutters regularly to remove dust, leaves, and other contaminates
Advantages/Disadvantages

Advantages

  • cost efficient technology
  • improves water quality by isolating water source
  • sustainable and reuses rain water instead of other water collection techniques
  • can utilize natural materials such as bamboo for pipes, recycled containers
  • keeps gray water lines separate from personal consumption water lines. (this is a source of many sickness in developing countries.)
  • Cultural acceptability-this technique of water catchments has been going on elsewhere for thousands of years.

Disadvantages

  • regular maintenance of gutter system
  • limited to annual rainfall per year
  • annual maintenance of water catchments
  • limited to one household per device
  • cautious to place rain water catchment devices in areas of heavy air pollution