Revision history [back]

I would say that while you may expect to receive 500,000 litres in a year you should also consider the rainfall pattern with respect to the usage pattern before sizing your tanks. Some parts of the country have two rainy seasons and others only get one, I'm not sure what the situation is at Tabora in the middle of the generally arid central plain.

You will need to use a pump anyway to raise water from an underground tank so you'll need to look at the construction practicalities and costings for all options before you decide whether to go for one, eight, or some other number of tanks. You need to consider where they want to pump water to as well as where the down-pipes are.

For roof water harvesting you should look at some mechanism on the down-pipes to remove the dirt and debris in the first flush of rain before diverting water into the tanks. The Centre for Alternative Technology (https://www.cat.org.uk/) may be able to provide appropriate information sheets or publications. With a couple of exceptions I have only seen plastic tanks used above ground. I have seen onion shaped cisterns dug out of solid rock in the West Bank and rectangular concrete lined ones in softer sediments. The entrance should be covered with a lockable man-hole to prevent unauthorised use of water and there should be a lip to prevent surface run-off from getting in. A good supplier of a variety of pumps in Tanzania is Davis and Shirtliff (https://www.dayliff.com/networks_content.asp?contentid=7&ct=Tanzania)

You may wish to get in touch with the Rainwater Harvesting Association of Tanzania (RHAT) which is a network of a variety of people interested in the subject. I do not have a contact in Tanzania but you can probably get in touch through the Southern and Eastern Africa Rainwater Network (SEARNET) at https://www.searnet.org/searnetfinal/home.asp or the Greater Horn of Africa Rainwater Partnership in Nairobi.

Regards

Martin Ager