563
edits
Changes
no edit summary
__NOTOC__
[[Image:akkerman.jpg|thumb|right|300px|A women using her water storage tank in Guinnee-Bissau. Photo: Paul Akkerman]]
Rainwater harvesting refers to structures which catch rainwater and store it in underground or above-ground tanks for later use. Any suitable roof surface — tiles, metal sheets, plastics, but not grass or palm leaf — can be used to intercept the flow of rainwater and provide a household with high-quality drinking water. Rainwater harvesting systems have been used since antiquity, and examples abound in all the great civilizations throughout history.
==Suitable conditions ==
Rainwater harvesting requires at least an annual rainfall of 100-200 mm. Many places in Latin America have rainfalls of about 500 millimeters per year. It is suitable even when the roof is small. For example a 5 x 6 meters (that is to say 30 square meters) house, with 500 mm annual precipitation, receives a rainfall of 15.000 liters on its roof; this is a sufficient amount for a family formed by 5 members. Storage tanks can also additionally be filled up by pumps.
{{procontable | pro=
==Technical specification==
====Storage tanks====
====Operation====
Roof rainwater is usually of good quality and does not require treatment before consumption. If the house has a chimney, it is however possible that the water becomes smoky. High chimneys are therefore preferred. Water is collected through roof gutters made of PVC, bamboo, etc. and stored. The most important thing to ensure water quality is a good lid, keeping out light and insects, and a filter, keeping out all kinds of dirt. Basic water quality testing is recommended during the first year, with further testing when water quality is in doubt. A low cost water test is the ‘HACH’ test, about US$1 per test. If contamination is suspected or when water quality needs to be guaranteed, the water can be treated in several ways.
Several pump systems can be used to lift the water from underground tanks, for example with a [[rope pump]] or with a [[deep well pump]], which can elevate water up to a height of 30 m.
====EMAS system====
The EMAS system for rainfall collection uses various EMAS technologies as well as simple tools to convert rainwater into usable drinking water. If roof rainwater is being used, it is collected through a regular gutter. To filter the water, at the bottom of the gutter, a pitcher or ferrocement tank is placed, with an outlet pipe. A synthetic cloth bag is attached to the rim of the pitcher using an iron ring or wire which fits around the edge. The bag should be cleaned every 3 months.
As water begins to collect, to avoid too much garbage collecting here, first some amount of water is deflected, along with most of the garbage. Hereafter, water can be directly sent to an [[EMAS cistern]]. It is advisable for multiple cisterns to be available for storage, depending on the size of the roof. Connect one cistern at a time to the outlet pipe. From here water can be pumped and distributed using a regular EMAS pump. The pump can also be connected to faucets and tanks around the house.
====Maintenance====
Removal of debris and overhanging vegetation from gutters and the roof, and preventing water from stagnating in is important to prevent the guttersgutter being clogged. Tank maintenance consists of physical inspection and repairing cracks with cement.
Several studies have shown that water from well-maintained and covered rooftop tanks generally meets drinking water quality standards if maintained rightfuly.
* [http://www.unep.org/depi/rainwater Rainwater Partnership ]
* [http://www.rainwater-toolkit.net/ Rainwater Toolkit]