The size of the tank you need for off-grid water depends on several factors, including your intended use for the water, the size of your household and your water demands, and whether the tank is your only water source or whether it's used alongside another off-grid water solution. We recommend using a 400-1,000-gallon water storage tank. If you're using a storage tank to deliver pressurized well water, it can be a lot smaller (20-120 gallons) because the well will provide a constant supply of water - the role of the storage tank is simply to prevent the well pump from being overused.