The factory watermaker on Lagoon is a Desalator Duo, dual voltage. They are the worst watermakers that I have had the pleasure of working on. We disable the 110-volt motor. It has to much torque, is mishandled by inexperienced operators. When the pressure is brought up to quickly destroys the clutches and belts. If the boat your chartering only has one tank that is because it was ordered without the extra tank. The water maker and spare tank are not mutually exclusive. The 42 in our fleet also has an aftermarket watermaker. This was done based on our experience with previous boats.