Rainwater Harvesting from Thatched Roofs
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Greetings to you,
Thanks for joining the newly formed group in rainwater harvesting that the Rain Foundation and RWSN recently set up. I just had a request from C at IFAD about experiences of Rainwater Harvesting from thatched roofs. He is interested in their applicability in the Pacific. C is a member of the rainwater group. Could anyone shed any light on this issue?
Is it worth considering huts at all, or is it a better option to look for institutions that have hard roofs?
To reply to the whole group as part of a discussion, just send a mail here (email on Dgroups site).
Looking forward to hearing from you,
There are a number of options for using thatched roofs for rainwater harvesting. Polythene coverings or other materials to reduce the permeability of thatched structures. The is usually capture of the runoff via gutters or tanks, as most thatched roofs do not usually have capture structures attached. Some information on designs, may or may not be of any use.
In the main hard roof areas (tiles, coated steel) are the better options as this provide better surfaces, that are easier to clean, but can also be used to calculate expected runoff from a known surface area (with low permeability) enabling you to design both gutter and tank capacity for the building. A simple model like RainTank2 can allow you to undertake rainfall-runoff calculations to determine demand-supply reliability curves relative to location and rainfall. Not sure that answered your question, Cheers Neil
The challenge we have is management of the quantity of water in the tank we have used many options but in vain others become rusty and the glasses are easily broken by children.
Uganda Muslim Rural Development Association (UMURDA)
Regarding measuring water quantity in a tank a simple option maybe be to install taps/ spigots in the wall of the at every 50 or 100 cm. By opening the tap you see if water comes out and so know the level maybe more "childproof".
Water quality in tanks.
If there is risk of contamination, tanks can be chlorinated of course but other options are filtering the water before use. There now are a number of effective low cost water filters like Stefani, SWACH, Tulip siphon, Safi filters with cost of 15-35 US$ and filter capacities up to 5 litres / hour.
Collecting water from Thatched roofs
Simple gutters made of roof sheet can be used and water collected in simple plastic, steel or cement tanks. A low cost foldable water tank is the so called BOB tank , cost 70US$ made in Uganda. Other low cost water tank is the so called wire cement tank, build with 1 bag of cement /m3 plus 1 kg or wire plus bricks or bamboo. If water quality is a problem use chlorine or low cost filters. Most filters nowadays also have activated carbon inside.
In areas with shallow water levels another option to collect water from Thatched roofs is to "inject" the water in the ground. Than with a hand dug or hand drilled wells and a locally made low cost hand pumps like EMAS or Rope pump the water can be pumped up.
Information on thes options can be found at websites of the SMART centres in Tanzania (SHIPO) and Malawi (Mzuzu) or other sites (see right).
Thank you very much for the links to the different sources of information on rainwater harvesting, all of which I found very useful and will keep for future reference. We were considering what the options might be for thatched roofs as we will be doing design of a project in July for very poor rural households in Kiribati where other materials may be too costly. From the information I could see so far though it seems that using the thatched roofs of houses probably isn't really a viable option.
I would like to get back to the group on this discussion and the Kiribati situation as we go ahead with our work to get more inputs later.
In the meantime, does anyone have a consultant with experience in rainwater harvesting in the Pacific islands to recommend? If so, perhaps you could write me directly, off-list, here (email on Dgroups site).
Thanks very much,
Dear C and N,
Did you not receive my reaction on your question about rainwater harvesting from thatched roofs in Guinea-Bissau (printed below)? We have good results in poor households, see my reaction from the 3rd of June:
I am the coördinator of a RWH organisation in Guinea-Bissau called: IAGU LIMPO-TABANKA SAN. We have observations of RWH from thatched roofs in the coastal areas of Guinea-Bissau, where the Balanta rice farmers live.
People collect water from thatched roofs in a traditional way, binding the ends of the thatch together, collecting it in available vessels and store it in the tank. The brown colour disappears during the storage as well as bacterial count goes down significantly.
You can read more about in the report of Hans Hartung: Rainwater harvesting in Guinea-Bissau.
In the pictures, you can see some examples, you see also an example with a sheet of plastic between 4 poles. That gives immediately clean water.
I hope this information can help you. Thank you and best regards,
Document and photo links on the Dgroups site for this conversation.
No I didn't receive the earlier reply, but thank you so much for sending, and then re-sending. The report and the photos and advice will all be very useful for us.