Abstract: A mobile water heating apparatus for rapidly heating large volumes of water, such as swimming pools, hot tubs, etc., at multiple sites includes a water heater, a water pump, and a water circuit comprising flexible conduit for direct coupling between the pool of water to be heated and the mobile water heating apparatus. The mobile water heating apparatus is independent of on-site dedicated facilities, provides rapid remote site service for cold weather or emergency situations, and is fully self contained, including energy source for heat generation and power generation for operating the water heating system equipment.