The water requirement of a specific model is usually expressed in gallons per minute (g.p.m.) and is listed in the unit’s specifications. Generally, the average system will use 1.5 g.p.m. per ton of capacity while operating, but the amount of water required depends on the size of the unit and the manufacturer’s specifications. Your contractor should be able to provide this information. Your well and pump combination should be large enough to supply the water needed by the heat pump in addition to your domestic water requirements. You probably will need to enlarge your pressure tank or modify your plumbing to supply adequate water to the heat pump.