Smaller tanks, such as the plastic (-barrel) are also used in some cases. Larger tanks are commonly used where there is no access to a centralised water supply. Companies recommend a tank for a house supporting two people (if compost toilets are placed) and if the region receives at least of precipitation a year. If it receives less (between , 2 or 3 of these 300-gallon tanks can be placed so that more rain can be gathered at times when it does rain. Also affecting tank size is predicted rainfall and rainfall variability; the higher prices for larger tanks; intended use of rainwater and typical consumption for these uses; the area of roof draining into the tank; security of supply desired.