It is probably more appropriate to ask why don’t you need an Eco Cistem given the global need to save water. Every toilet needs a cistern and Eco Cistem uses a water source currently considered a waste product to flush toilets, thus reducing the requirement to use and flush away fresh drinking water. Using mains fed water also costs money every time a toilet is flushed. Eco Cistem can reduce or even remove the cost of flushing a toilet.