Cisterns are commonly prevalent in areas where water is scarce, either because it is rare or has been depleted due to heavy use. Historically, the water was used for many purposes including cooking, irrigation, and washing. Present-day cisterns are often used only for irrigation due to concerns over water quality. Cisterns today can also be outfitted with filters or other water purification methods when the water is intended for consumption. It is not uncommon for a cistern to be open in some manner in order to catch rain or to include more elaborate rainwater harvesting systems. It is important in these cases to have a system that does not leave the water open to algae or to mosquitoes, which are attracted to the water and then potentially carry disease to nearby humans.