Rainwater Harvesting

General Guidelines for Collecting Rain Water 

  • Roof: 10mm of rainfall on a surface area of 100m2 will yield 1000 litres of rain water.
  • Gutter & downpipe: Essential for capturing and guiding rainwater into tank. Ensure gutters are cleaned from time to time!
  • Tank: Use a good quality tank, preferably with black lining, to prevent growth of algae.
  • Filtration: 
    Before: Keeps rain water clean and odourless - use a Pre-Filter (see below), or other options such as: Water Rhapsody Rain Runner | Sinvac First Flush Diverter | First_flush_bucket.
    After: Use a layered filter system that adds in essential minerals and cleans the water, such as Water Well Mineral Pot
  • Overflow: Attach a thick black pipe to overflow outlet, use an adaptor to connect it to hose-pipe 
  • Connect to household: Your rainwater supply can be plumbed into your household water reticulation system.  
  • Rain Tank Care Info

Rain Water Tank Pre-Filter

Filter roof water before it enters the tank to keep your tank free of debris, mosquitoes, rats and other unwanted items that will decompose and pollute the water. Nikki's low-maintenance, dome-shaped pre-filter needs the following:

  • 1 x support ring (flat, approx 2cm wide, 21cm outside diameter), stainless steel;  
  • 4 x bolts, nuts & washers, stainless steel;  
  • 1 x coarse support mesh, round (approx 21cm diameter), dome-shaped (approx 5cm at highest point), stainless steel (the head of a large, Chinese style kitchen strainer is ideal);  
  • 1 x round piece of fine mesh (approx 24cm diameter), grade 316 stainless steel (0.406mm hole x 0.17mm wire strand);   
  • 1 x tube of marine grade silicone sealant.  

Note underside view of pre-filter, secured in place in the rain tank lid.  

Rain Water Tank Pre Filter underside

  • Cut a hole in the rain water tank lid, approx 19cm diameter;

  • Drill 4 holes in the support ring, for the bolts;
  • Cut a circular piece of fine mesh, approx a 24cm diameter;
  • Fit the fine mesh over the dome-shaped support mesh, folding it carefully over the rim, clamp to keep the folded fine mesh in place under the rim of the support mesh; 
  • Using the 4 holes in the support ring as a guide, drill smaller holes through the fine mesh and through the tank lid;
  • Place the support ring against the underside of the tank lid, and the mesh structure above, with the holes correctly aligned; 
  • Secure the filter to the rain water tank lid with the bolts, nuts & washers;
  • Silicone seal all around the edge and fill any gaps.
  • Ensure the gutter downpipe is suspended at least 20cm above the pre-filter system, to allow space for debris to slip off or blow away.


  • Because of the dome shape, most debris should slip off the pre-filter.
  • Do a visual check from time to time, especially after rain.
  • If any debris is present, sweep off lightly with a soft broom. If necessary, remove the tank lid and sweep the pre-filter with a soft brush under running water. Replace immediately. 


Health Considerations

Rainwater is considered to be a safe source of drinking water. Almost no accounts of illness are associated with drinking it.

  • Mineral content: Depends on local air quality, generally 'soft' (low mineral content). 
  • Use a layered filter system that adds in essential minerals (and cleans the water), such as Water Well Mineral Pot
  • Mosquitoes: Keep out with a pre-filter.
  • Rats: Keep out with a pre-filter

More Info


Last Modified: Fri, 17 Jan 2020 14:09:18 SAST