Gauteng and NW Province

Harvest your rainwater

By Marlene McKay

Did you know that more than 80% of rainwater evaporates back into the atmosphere? When water evaporates through plants, (transpiration) it cools the atmosphere and biological diversity increases.

Rainwater harvesting is not only a way to make the most of nature’s gift, but containing runoff from your roof and paving will also help improve the overall condition of our rivers and dams plus this recharge of groundwater feeds wetlands. “Runoff from hard surfaces,” said Petrus Venter, Water Affairs Programme Leader of the Hartbeespoort Dam Integrated Biological Remediation Programme, “picks up energy as it rushes away and through storm water pipes to the rivers. This increases erosion and reduces groundwater recharge.

By using simple rainwater harvesting techniques, the severity of this impact can be significantly reduced.”

The ancient soil of Southern Africa is blessed with different types of vegetation that substantially increase rainwater absorption.

Desertification caused by urban, mining and agricultural activities increase hard surfaces and quick runoff. Roads, paving and buildings do not allow for the infiltration of water and instead rain is forced directly into streams and storm water runoff drains. This causes erosion and siltation, which pose major challenges in the Hartbeespoort Dam and the upstream catchment.

The increased runoff also reduces groundwater recharge, which lowers the water table and reduces the recharge to streams as well as wetlands.

Harvesting rainwater makes sense as it substitutes potable and irrigation water. “Rainwater harvesting also supplements the subsoil water level and provides the opportunity to increase urban greenery,” said Sameer Morar, the Rand Water project manager for the Hartbeespoort Dam Remediation Programme. “Urban greenery also assists with cooling our urban deserts and might even increase rainfall.”

The benefits of rainwater harvesting are endless and it is important to remember that the responsibility to conserve water lies with each of us.

“Water supplies are increasingly under pressure and it is one of the most essential factors for our continued existence on this planet. In addition, a store of rain water ensures that you have emergency water when next the water supply is interrupted or water restrictions are enforced,” Morar said.

Harvesting systems are easy to construct, but it is important to remember that roof rainwater often requires further cleaning before drinking as it may contain dirt or remains of bird droppings.

However, untreated roofwater is useful for flushing toilets, washing clothes or cars and watering the garden as these uses amount to about half the water consumed in an average household.

Rainwater storage tanks can be constructed from a more aesthetic material such as cement and must be covered to prevent mosquitos from breeding in the water and to reduce evaporation, contamination and the growth of algae.

You’d be amazed to realise the significant amount of rainwater that can also be contained in the soil through the contouring of your garden with swales and berms. This greens your garden as it will require less water and perhaps you will be able to sustain more trees and less grass and paving.

Kormorant May 2012

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