How a Crew of Twenty Makes Its Own Water for Nine Months

A container ship leaves port with nine months of food in her stores and almost no drinking water aboard. That isn't an oversight. Water is the heaviest thing a ship could carry and the one thing she can't carry enough of, so she doesn't try. She makes it instead — every day, out of the sea she is floating in, in a machine most people on board never look at twice. The principle is old and simple. Take seawater, boil it at low pressure so it turns to vapour at a temperature the engine's own waste heat can reach, let the salt stay behind, condense the vapour back into fresh water and run it into the tanks. A crew of twenty gets its showers, its coffee, its cooking water and the water in the engine cooling system out of that one process, running quietly below decks while everyone sleeps. What makes it worth understanding is how narrow the margin is. The machine only works while the main engine is running hot, so a ship