Components of rainwater harvesting
The components of domestic rainwater harvesting are as follows:
(a) Catchment (b)Conveyance (C) Filtration (d) Storage unit (e) Recharge unit.
The roof of the house is used as a catchment for collecting rainwater. The type of roof may be sloping or flat. It may be constructed with suitable roofing material. Corrugated iron sheets, asbestos sheets, PVC sheets, tiles or concrete slab are suitable for rainwater harvesting.
The conveyance system consists of a pipeline or drain that carry rainwater from the catchment to the filtration and storage unit or the recharge unit. The open channel known as gutter is fixed to the edges of the roof to collect and transport the rainwater. Gl Sheets, cut PVC pipe or split bamboo can be used for gutter. While fixing the channel, proper support should be given and appropriate slope should be maintained.
The down pipe is also a unit of conveyance. It should be made up of PVC, Asbestos Gl or Bamboo pipe. The pipe should be of 50- 75 mm in diameter. There should be arrangement of flushing of first rainfall water, as it is generally contaminated.
(c) Filtration Unit:
Filtration unit consists of a chamber filled with media such as coarse sand charcoal, coconut fibers of filter screen, pebbles and gravel. As an alternative fine cloth in two of three layers can be tied with the down pipe to act as filtering medium. It is desirable to change the filter medium before onset of monsoon.
(d) Storage Unit:
The storage unit may be in form of a vessel , big drum and water storage tank at ground level or below ground level. Storage unit should be sufficiently large to meet the domestic water needs. In the region where rain falls throughout the year, a small size water tank, vessel or big drum will be sufficient but for determining size of storage unit in other regions, it is suggested to make assessment of domestic water need considering the size of family and the period of acute shortage of water.
The storage water tank can be made up of tin, PVC or masonry construction. Water tank on the ground facilitates easy withdrawal of water however it occupies usable space. Where space is a constraint, underground water tank can be preferred. There should be sufficiently large manhole so as to facilitate cleaning of the tank. The manhole cover should be airtight. Under no circumstances there should be uncovered openings otherwise it will become a mosquito-breeding place.
(e) Recharge Unit:
Recharge unit is used to enrich the aquifer with rainwater. Structures like dug wells, bore wells, recharge trench and pits in the vicinity can be used for recharging of aquifer.
Quality of harvested rainwater
Rainwater collected from rooftop is generally free from pollutants and dissolved salts and is of good quality. However due care should be taken to remove dust and dirt, leaves, bird droppings, pieces of paper etc., from the rooftop and the open gutter, otherwise will settle if collected water is not disturbed, Biological contamination can be removed by disinfecting the water. Boiling water for 10-20 minutes is sufficient to remove biological contaminants. Domestic filters can also be used to purify water.
(To be concluded)