Rainwater Harvesting

Rhodes University has started a programme of installing 5000 litre tanks to harvest rainwater off all residence roofs on campus. The student society, Galela Amanzi, raises funds to install rainwater tanks in Grahamstown East. Many residents in Grahamstown are also installing rainwater tanks at home. The following need to be in place:

• Roof: 10 mm of rainfall on a surface area of 100 m² will yield 1000 litres.
• Gutter & downpipe: Essential for capturing and guiding rainwater to your tank.
• Tank stand: A correctly constructed base provides stable support; if possible, allow sufficient space for a bucket under the tap.
• Rainwater tank: Use a good quality tank, preferably with black lining to prevent growth of algae.
• Filtration: Debris and dust on the roof may be filtered in a variety of ways. If water is filtered before it goes into the tank, the water remains clean, odourless and does not need to be cleaned out (dirt, debris, droppings, rats and mosqitoes are excluded, and anaerobic microorganisms will not grow in clean water).

Simple, low-cost Top_filter_sieve_system:

1. Cut a 25 cm diameter hole in the rainwater tank lid;

   
    Fine flat sieve beneath coarse convex sieve

2. Fix a flat fine sieve ("stainless steel 316 mesh" does not rust, available at engineering outlets) over this hole (to catch very fine dust & dried bird droppings, exclude mosquitoes);
3. Fix convex coarse sieve on a hinge above fine sieve (items like leaves & twigs bounce off; also excludes rats);

   
   Downpipe suspended above sieve system

4. Suspend downpipe approximately 12 cm above the 'filter system' (as water emerges, there is space for debris to bounce away).
5. Maintenance: About once a year, remove lid and gently scrub the fine sieve with a brush and water to remove dirt.

• Overflow: Attach a thick black pipe to overflow outlet, then an adaptor to connect it to a length of thin hose-pipe (guided into any part of garden as desired; long thin pipe prevents unwanted creatures entering tank).

  
  Black pipe on overflow outlet

• Tap: A brass tap on outlet allows attachment of hosepipe if required.

Other options: You may prefer the Hydro Dynamics First Flush Diverter, or Rain Harvest First Flush Diverter , or make your own First_flush_bucket.

More INFO

• Roofwater Harvesting: A Handbook for Practitioners by TH Thomas and DB Martinson (2007)
• Rainwater Harvesting research at the University of Warwick
• Rainwater Harvesting conference paper

From a health point of view, rainwater is considered to be safe source of drinking water. There are almost no accounts of serious illness associated with drinking it.

• Asbestos: The long-term consumption of rainwater harvested via asbestos roofs, gutters or tanks is not linked to asbestos-related disease. More info: long-term research findings, asbestos affects mainly lungs, EPA proposed concentration, asbestos natural occurrence,
• Bird droppings: The risk of contracting disease from bird droppings is negligible, as any avian enteric organisms will be rapidly denatured through heat and dehydration on the roof. More info: conference paper, Civil Research Group.
• Mosquitoes: The risk of mosquitoes breeding in the rainwater tank is usually eliminated by the Top_filter_sieve_system above.
• Rats: The risk of rats entering the rainwater tank is eliminated by the Top_filter_sieve_system above.

Go to the Rhodes University ENVIRONMENT front page. Suggestions/Questions? Contact environment(at)ru.ac.za