In the event of salinity of the fresh water density exceeding a pre-determined value the (maximum usually 4 p.p.m.) the solenoid controlled dump valve diverts the flow to the bilge, preventing contamination of the made water. Excess salinity could be caused by sea water leakage at the condenser or the evaporator priming, the former is the most likely. Feed supply rate to the evaporator is fixed by the orifice plate and sufficient water goes to the ejectors to ensure a high vacuum condition in the shell at all times and that a brine is easily dealt with.