How to convert rain into safe drinking water

Water and sanitation

In rural areas, the main water sources are normally groundwater borewells or surface water, rivers and lakes. However, an often overlooked, easily accessible and sustainable source of safe drinking water during the wet season is rain. In tropical and sub-tropical climates the quantity of water collected from rainfall can be substantial. 

Putting the finishing touches to a rainwater harvest tank in Uganda that saves a four-hour walk to collect water. Photo: Marcus Perkins/Tearfund
Putting the finishing touches to a rainwater harvest tank in Uganda that saves a four-hour walk to collect water. Photo: Marcus Perkins/Tearfund

There are clear advantages to rainwater harvesting at home: 

  • improved health 
  • easy access 
  • low cost
  • it is easy to manage. 

Traditional rainwater harvesting 

Traditional methods of rainwater harvesting used in Uganda and Sri Lanka include rainwater collection from trees, using banana leaves or stems as temporary gutters. Up to 200 litres may be collected from a large tree in a single storm. 

Rooftop rainwater harvesting 

Very low cost domestic rainwater harvesting systems can be easily installed on most corrugated iron or clay tile rooftops in rural and urban areas, using various forms of guttering, first flush diverters (a pipe system that diverts the ‘first flush’ of contaminated water away from the container, and then allows the rest of the rainwater to be directed into the container - see a diagram here) and plastic or ferro-cement tanks for collection and storage. 

Rainwater harvesting without rooftops 

However, in some rural areas most people live in simple thatched roof structures, which are not suitable for traditional rain - water harvesting. Tearfund has therefore researched and tested an innovative and simple ‘ultra low cost’ way of harvesting rainwater without using rooftops. 

Using plastic sheeting 

In many populations on the move, especially in emergency and post-emergency situations, plastic sheeting is a basic commodity that many households own. It is either given through distributions at refugee camps or camps for internally displaced persons, or purchased on the local market. Plastic sheets are used for many purposes including as shelter for homes or shops. They can also be used for rainwater harvesting. Calculations based on rainfall data from Colombo, Sri Lanka, show there would be an average daily yield of more than 60 litres over six months of the year from rainwater harvesting using an 8m2 plastic sheet for collection. 

A rainwater catchment tank in Uganda makes all the difference to the availability of safe, clean water. The writing on this one reads: 'Jesus is good and He has given good water'. Photo: Tim Raby/Tearfund
A rainwater catchment tank in Uganda makes all the difference to the availability of safe, clean water. The writing on this one reads: 'Jesus is good and He has given good water'. Photo: Tim Raby/Tearfund

Designing your own rainwater harvesting system 

Using plastic sheeting is one option for rainwater harvesting without using a roof. Other locally available materials can also be successfully used, such as single corrugated iron sheets and cloth. 

There are no rules for construction. Think of new ideas using whatever materials you have available to catch and collect the rainwater. The principle is always the same: 

Catch the rainwater on a clean surface before it hits the ground, and channel into a clean collection container. 

Scaling up 

It is easy to scale up rainwater harvesting systems. In emergency situations, rain­water harvesting can be made available to all and can even contribute as a significant water source in large communities and camps. Remember to promote good hygiene at the same time, making sure that each part of the system is clean. Cover the water container and make sure the stored water is not removed by dipping hands or scooping using dirty cups or other dirty items. Rainwater which has been stored for a long period may require disinfection. Protect water containers with a screen to stop mosquitoes breeding and keep out sunlight to prevent the growth of algae. 

This article appears in issue 82 of Footsteps magazine, which is on the topic of natural resources. You can read Footsteps online, sign up to receive Footsteps regularly or contact us to order printed copies.

Murray Burt
Murray Burt is a chartered civil and environmental engineer with 20 years experience in commercial engineering consultancies, governmental and non-governmental organisations in Africa, Asia and Pacific. He is Global Senior WASH Officer for UNHCR, where he oversees the delivery of water, sanitation and hygiene services to refugees around the world.