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RAINWATER HARVESTING FOR POTABLE WATER SUPPLY

To be climate resilient, it is important to utilise and diversify water sources. Rainwater harvesting can provide an alternative water source by collecting and storing rainwater falling on rooftops. The collected rainwater can either be stored in tanks or used to recharge groundwater. Rainwater can be harvested from roofs made of up different types of materials such as thatch, metal, tiles and mud.

Image removed.A rainwater harvesting system at the household scale normally has four key components:

  • Conveyance system – gutters and downpipes that channel the water from the collection surface into a rainwater tank
  • Diverters and filters – to keep leaves and other debris out of the storage tank
  • Storage tank – to safely store the water that has been collected.
  • Distribution system –pumps and pipes used to transport the water from the tank to wherever it will be used

Rainwater harvesting can have a triple benefit in more built-up urban areas of the Pacific. Firstly, it reduces the costs of water infrastructure (i.e. treatment and distribution systems). Second, when combined with water efficient appliances it can also reduce household expenditure on water. Finally, rainwater harvesting can reduce stormwater management costs as the water is captured and consumed rather than diverted to stormwater systems.

  • Rainwater harvesting can be a cheaper alternative to centralised water supply systems.
  • If maintained properly, the system can work for more than 20 years.
  • Rainwater harvesting reduces use of expensive fossil fuels as there is limited need for water treatment and pumping.
  • Rainwater harvesting can decrease local scale flooding as stormwater is stored instead of being directed to runoff.
  • Some Pacific Islands may not have the facilities or materials to manufacture the equipment required for rainwater harvesting. Reliance on importing materials can cause delays in implementation (as highlighted in the case study below).
  • In remote islands and rural communities, many households use thatched houses that do not collect rainwater.
  • Regular testing of the water supplied by a rainwater harvesting system is needed to ensure appropriate quality.
Indicative cost

Rainwater harvesting is relatively low compared to centralised water supply systems. Whilst providing cost estimates is difficult given the broad range of influencing factors across the Pacific, the below table outlines the key components that should be taken into account when estimating rainwater harvesting project budget for a specific location.

Components

Unit
(A)

Number of units (B)

Unit Cost
(C)

Budget
(B x C)

Establishment Cost

        
  • Planning and design including community outreach

e.g hours

      
  • Materials (e.g. pipes, tanks)

e.g. number

      
  • Labour

e.g. hours

      
  • Reporting to donor (if required)

e.g. hours

      

Ongoing Cost

        
  • Maintenance Cost (materials and labour)

e.g. number and hours

      
  • Reporting and Monitoring

e.g. hours

      

Rainwater harvesting can be compared against conventional water supply systems which are heavily dependent on centralised infrastructure (e.g. laying of pipes and use of wastewater treatment plants). Comparisons between the two approaches include:

  • The decentralised nature of rainwater harvesting provides greater resilience as communities are not all reliant on one system for their water supplies.
  • Conventional water supply systems incur larger infrastructure and energy costs.
On-ground impacts that the EbA option addresses
Decreasing water availability
Poor water quality
Increased frequency of flooding

Case study

Improving Domestic Rainwater Harvesting Systems

Niue

The Pacific Adaptation to Climate Change (PACC) project is building climate resilience in Niue by improving the country’s water resource management. As part of the project, rainwater tank manufacturing plant design and implementation was undertaken and rainwater harvesting systems provided to eligible households. After an initial piloting, the project was extended to all 14 villages on the island.

Initially, the communities were not motivated to be part of the project as they were already connected to a water supply at no cost, therefore a robust communication strategy was devised. Three communication campaigns were delivered:

  • A water conservation campaign – fix the leaks
  • A water protection campaign – Keeping Niue’s water pure
  • A rainwater tank safety and maintenance education campaign – this was specifically developed by the PACC project to provide training and awareness on maintenance of rainwater harvesting systems at the household level.

By end of the project, 420 households had installed 5,000 litre tanks to improve water access. Out of the 420, around 250 households improved guttering and flush diverters and connections to rainwater tank as well. The 5,000-litre tanks provide an additional 16 days of water supply for each household (assuming 3-person household and an average of 100l per person per day demand).

Reference: PACC Demonstration Guide: Improving domestic rainwater harvesting systems in Niue,  https://www.sprep.org/attachments/Publications/CC/PACCTechRep14.pdf