The correct answer is A) Cycling the potable water pump on and off by the action of the potable water hydro pneumatic tank pressure switch in response to system demand changes. This is the correct answer because on most commercial cargo vessels with a small crew and limited potable water usage, the potable water system pressure is typically maintained through the use of a hydro pneumatic tank. As the system demand changes, the pressure switch in the tank will cycle the potable water pump on and off to maintain the desired pressure range, rather than allowing the pump to run continuously. The other options are incorrect because B) and C) describe methods more suited for larger potable water systems with higher demand, while D) utilizes tank level switches instead of the more common pressure switch approach.