Toward Increasing Rainwater Use in the 21st Century

By Dr. Shelly Rodrigo, PhD
September 27, 2011

The International Decade for Action ‘Water for Life’ began in 2005 and ends in 2015. Water plays an important part in human life and three Millennium Development Goals (MDG) for 2015 have been established:

  • to reduce by half the proportion of people without access to safe drinking water by 2015;
  • to stop unsustainable exploitation of water resources;
  • to develop integrated water resource management and water efficiency plans; and
  • to halve the proportion of people who do not have access to basic sanitation (UN Water, 2009).

The success of the MDGs are in jeopardy since many countries still suffer the pains of water scarcity, with drought ravaging the African continent and, closer to home, water shortages are experienced in parts of the Caribbean.

Rainwater has a long history of use in the Caribbean, however with the advent of regulated mains water supplies, usage decreased in urban areas. In rural areas and areas where squatting occurred, rainwater is still being collected and used as the main domestic water source. Historically until the 20th century, rainwater was one of the main supplies used domestically especially in developing countries. Over the past few years there has been a movement toward the re-uptake of rainwater as a domestic water source; however there are many obstacles to its use, either from the public or health and water authorities. The main argument by detractors is that rainwater does not represent a safe supply and hence there may be a potential health risk over a lifetime of consumption. However, the safety of rainwater, especially as a drinking water source, depends on the management and maintenance of the harvesting system.

Rainwater may be used for drinking if good practices are employed in the management and maintenance of the rainwater harvesting systems. In areas where drought is currently occurring and in others where water shortages occur frequently, use of rainwater can reduce the gap between supply and demand for drinking water.  Alternatively where consumers and/or health authorities are not in favor of rainwater for drinking, the water can be used for laundering, bathing, flushing toilets and car washing.

If you are considering a new dwelling, then you can build a cistern (underground tank) which can be plumbed into the toilet and used for non-drinking purposes. For those with an existing house, buy a poly tank that can collect rainwater. Plumbing this tank into the toilet can reduce the amount of drinking water that is used.

For those interested in collecting rainwater for use when the mains supply is low, you can improve the quality of the water supply by doing the following:

  1. Use of materials that would not leach into the rainwater tanks for the catchment surface, gutters and rainwater tank. The materials generally used today in tank construction include colorbond, zincalume and concrete.
  2. Removal of trees overhanging the catchment surface thus minimizing access to the catchment surface by small animals and birds perching on the overhanging branches.
  3. Installation of gutter guards and screens which limit collection of plant material into the rainwater system.  This has an impact on the solubility of metals such as lead, if plant material is present in the tank, metals become more soluble. Lead can result in chronic or acute damage to the nervous system, cause harmful effects on the kidney, gastrointestinal tract, joints and reproductive system, and problems in the synthesis of hemoglobin.
  4. Use of first flush devices which prevent the first washings from the catchment surface from entering the tank. This action would limit the amount of sediment and the level of chemicals (in the case of chemicals deposited on the catchment surface due to agricultural spraying etc.) and biological contamination in the harvested rainwater.
  5. Collection of rainwater in a secondary tank to allow sedimentation to occur. Sedimentation has been shown to reduce contaminant levels in the soluble phase of the rainwater tank. When a combination of tanks is used, with water being drawn off from the collecting tank, the health risk is minimized.
  6. Installation of filters on the line leading from the tank into the house; or alternatively on the lines leading to the kitchen and bathroom sinks to increase the quality of the rainwater used for drinking.
  7. Removal of sediment build-up every five years. Sediment has been found to contain metal levels, depending on the tank, gutter and catchment materials, comparable with that of industrial waste.

Harvesting rainwater offers a level of protection to the population of a country when water shortages occur due to the limited mains water supply. Harvesting rainwater can also reduce storm water damage in flood-prone areas. This practice of rainwater harvesting has been widely implemented not only in developing countries, but many developed countries are noting the wisdom of the re-introduction of such systems. Construction of new homes should consider designs whereby rainwater systems can be used as a water source. For those in the Caribbean region who wish to learn more about rainwater harvesting, a good resource is the “A Handbook on Rainwater Harvesting in the Caribbean” produced by the Caribbean Environmental Health Institute.

References:

UN Water. 2009. International Decade for Action: Water for Life, 2005 – 2015. 2006. Available from: http://www.un.org/waterforlifedecade/background.html.

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