HEALTH AND SANITATION 31
“ For example, if the toilet demand on X building was 3 750 litres a day, how many days in the year would the building have enough water to supply 100 % of this daily demand?” he said.
He suggested one of the most underappreciated benefits of rainwater catchment systems is their ability to manage stormwater by slowing the release of runoff during heavy rain events. While this concept is intuitive to those in the industry, it can be difficult for the general public to grasp. He explained that when rain is captured in a tank and released gradually after the storm has passed, it helps prevent creeks, streams and rivers from becoming overwhelmed. In urban environments, however, water runs off quickly from impervious surfaces like roofs, roads and sidewalks, leading to increased flooding and erosion.
Van Giesen recounted how he explained this at his church, where a small rain tank had been installed. Although people initially struggled to see the value, once he laid it out clearly, they began to understand the environmental impact.“ Most people are smart enough to understand the concept if it’ s explained to them the right way,” he said.
Design process is critical Van Giesen said no single design element ensures a rainwater harvesting system is safe and effective – what matters most is how all components function together as a cohesive system.“ The rainwater system, by definition, is not necessarily the sum of its parts. They have to work together.”
The next critical component is the inlet pre-filter, typically a gravity-fed screen that removes larger debris such as leaves, acorns or roofing grit before water enters the storage tank. Without this filtration step, tanks can accumulate organic material and other contaminants that degrade water quality and complicate treatment.
Proper tank design is equally important. Key considerations include blocking sunlight to prevent algae growth; restricted access so people don’ t open the tank, drop or throw items like tools inside, or accidentally fall in; and providing –‘ water in, air out’, he said. It’ s also important to keep the tank out of direct sunlight, because hotter water can promote the growth of bacteria such as Legionella. Materials used for the tank and other components must be non-leaching, especially when the system is intended for potable water use.
From there, the system must include appropriate pumping and filtration tailored to the water’ s end use. For example, water intended for irrigation may require less treatment than water used for indoor applications such as toilet flushing or cooling towers.
In some cases, pH adjustment may also be necessary, as rainwater tends to be slightly acidic depending on the region of the country.“ Remember, rain does not equal rainwater. Rain is what is in the atmosphere before it hits the surface. Rainwater is after the rain hits the surface and runs off it because it’ s going to continue to pick up contaminants,” Van Giesen said.
The design process begins with the collection surface— typically the roof. Van Giesen stressed the importance of inspecting the roof for debris, chemical residue or deterioration, all of which can affect water quality depending on the intended end use. A deteriorating or neglected roof can introduce pollutants that downstream filtration may not be able to handle effectively.
Finally, Van Giesen emphasised the importance of system scalability and understanding usage patterns. Unlike a residence with consistent demand, commercial or institutional facilities may experience highly variable water use. A system serving restrooms in a university auditorium, for instance, must account for periodic spikes in demand when events are held.
August 2026 Volume 32 I Number 06 www. plumbingafrica. co. za