An electrochemical engine for a vehicle comprises a fuel processor operating to process liquid fuel to hydrogen gas reformate, a combustor to generate heat for the fuel processor, and a fuel cell stack to generate electricity from the hydrogen gas reformate and producing water vapor by-product. A water management system of the engine comprises a condenser to reclaim liquid water from the water vapor by-product and a water tank for storing the reclaimed water. A water pump circulates water from the water tank to the fuel processor. A drainage valve is operable to open to release water from the water tank to a freeze tank to avoid freezing water in the water tank.