If surface water is used as an alternative for drinking water, quality and availability are important factors. In addition, the water balance of the surface water may not be disrupted adversely by the withdrawals. The quality of surface water differs substantially from one situation to the next; in each instance, the water will have to be tested to determine whether it can be used to replace drinking water for a particular purpose.
As a rule, the quality will be poorer than that of rainwater or groundwater: the water is often unclear as a result of the presence of algae or other pollutants. Most surface water can therefore only be used for low-grade purposes such as flushing toilets and watering the garden.
The benefit of using surface water as opposed to using rainwater is that no reservoir needs to be installed. To ensure a closed water balance, the rainwater can be drained from the site and the roof surfaces and into the surface water.