Climate change and rapid urbanization have meant there is increasing pressure on water supplies in cities and towns in South Africa. This has lead to water shortages and unreliable supplies.

It is, therefore, becoming increasingly important to understand whether there are alternative sources of water which can be used to improve the resilience of supply. One solution is to develop onsite rainwater harvesting systems.

These systems capture rainwater from roofs and other surfaces and store this. Stored water is then available to be used instead of municipal water supplies for drinking, cleaning, irrigation and flushing toilets.

In a new paper, I explore the implications of developing off-grid rainwater harvesting systems for existing houses. In the case study, I show that water neutrality can be achieved, even in areas with a dry season of over 4 months.

However, this has implications including a requirement to be water-efficient, having access to a large catchment area and setting aside significant space for rainwater tanks. The financial analysis also shows that the water-neutral rainwater harvesting systems can have long pay-back period.

These considerations should, however, be balanced by increased resilience to water outages and the avoidance of the disruption, potential health risks and costs of emergency water supplies here.