Rainwater Harvesting

Author: Sean Dowds and Walter Penfold - Rainharvesting Systems (PTY) Ltd

( Article Type: Explanation )

Rainwater harvesting is the practice of collecting rainwater or stormwater, and storing it for subsequent use either indoors or outdoors. The most common form consists of harvesting rainwater from roofs or paved surfaces, but it can also be collected through specially prepared porous ground surfaces or via subsoil drainage from turf areas. Rainwater can be used in just about any application if it is filtered and treated appropriately. Common uses include landscape irrigation, pool filling, car washing, clothes washing, toilet flushing, showering and bathing, industrial cooling, and where regulations and tests allow it – drinking water.

      Humans have harvested rainwater since times immemorial. The ancient Romans built houses with rooftops specifically designed to catch rain and store it for general household use. The advent of central pressurised water supply systems largely did away with the need for rainwater harvesting in urban areas as people became accustomed to water on tap as the norm. There has been a revival of urban rain harvesting in the past few decades as population pressures and increased cycles of drought and flood have put increasing strain on our water resources. The high cost of centrally supplied water, in both economic and environmental terms, has also driven people to consider more cost-effective and sustainable methods of water supply.

Polluted runoff water infects our rivers and dams
Nature designed the majority of rainwater to filter through the earth into groundwater systems and a smaller portion to flow over hard surfaces into rivers. In cities and urban areas the proportions have reversed with most water now running over roads and paved surfaces into storm water systems. As these surfaces are frequently polluted by oil, petrol and garbage, this severely affects the quality of our water as it becomes concentrated with pathogens, toxins and pollution from the surfaces it runs off. In addition, the storm water infrastructures built to manage runoff water are often overwhelmed as we constantly expand the area of our concrete jungles. Unusually high rates of precipitation add to the destructive force of water when our man-made systems fail. Relentless torrents of storm water have washed away bridges and cars and caused massive damage to property and human lives. This also causes flooding and irreparable damage to ecosystems downstream.

The Carbon footprint of operating, maintaining and expanding our central water systems
The polluted runoff water directed by stormwater systems into our waterways eventually finds its way to collection dams. After extensive cleaning and treatment from the dam to the treatment plant, it is dosed with chemicals, until the water is deemed fit for drinking. It is then pumped many kilometres to our homes and businesses, consuming vast amounts of energy along its journey. Most of this drinking quality water is then flushed down the toilet or drain or used for irrigation and only 5% is actually used for drinking or food preparation purposes.

Escalating water costs
Whilst water has been one of the cheapest, commodities it is highly likely that water will escalate at between 10-15% over the next few years, because many of the input costs (such as electricity) are likely to increase at an even faster rate. Since a large portion of our water is given away for free (first 6kl per household), the increased costs will have to be recovered from the upper tariffs. This could cause significant price hikes for the average urban household or business in the next few years.

The future of rainwater harvesting in South Africa
While it has historically had an important place in rural and drought-stricken areas in South Africa, rainwater harvesting provides an important solution to reducing the environmental impact of urbanization and a cost effective way of reducing the need for a central infrastructure to supply water to all the inhabitants of South Africa. It is something that every person in the country can do to improve the quality and sustainability of our water supply for future generations. To encourage this practice it would be helpful if government policy supported it through rebates and incentives