The water pump is used to pump water from the tank to the fixtures. If you don't have a tank you don't need a pump, however if away from hook ups you will be operating out of jugs..
You may have to block the lines that would have gone to the pump to have a watertight system when hooked up. The pump itself usually has a check valve
Rick Davis 1602 K8DOC
61 tradewind, plus a few others
13 Ram 2500 TD
99 Dodge TD 577K miles