Having been frustrated for some time with existing methods of designing rainwater, I have developed a new methodology and tool called the Rainwater Use Model (RUM). The development of the RUM was a result of looking at current methodologies which did not address questions like:

• How large should a rainwater tank be?
• Is the catchment area big enough?
• Will harvested water meet needs, even over a long dry period?
• How do you take into account variability in rainfall between years?
• How do calculate water needs?
• Given the choice, should you invest in larger rainwater tanks or a larger catchment areas?
• What is the payback of rainwater harvesting systems?
• How can you estimate the contingencies and reserves provided by a rainwater harvesting system?

The RUM answers these questions and having tested it on a case study house in Pretoria, South Africa aiming to be ‘water-neutral’ the approach appears far more accurate than existing methodologies. The results are being written up in a paper and the tool has been developed with a simple manual for dissemination. Contact me if you would like more information.