What if the water is dirty or unsuitable?
Wastewater that comes from cities, or has been used for agriculture or industry, often contains contaminants that make it unsuitable to re-use. Sewage effluent and industrial discharge is usually treated before it is put into aquifers, meaning that the level of contaminants is low to begin with. For stormwater, passive treatment in wetlands is sometimes the only pre-treatment needed. But one of the interesting side effects of ASR is that it can naturally clean up the stored water over time. When the water is injected underground it is no longer exposed to oxygen and geochemical and microbiological changes occur, and natural micro-organisms can kill disease-causing organisms. It is a form of natural biological control ensuring that, over time, nearly all of the harmful organisms are removed from the water. In the right kind of situation, stormwater that is recovered from aquifers could even be suitable for drinking.
