Alchemy in the Desert? explains the “market” for water-extraction equipment:
The military calculates that a soldier in the desert needs about 20 gallons of water a day, five of which must be pure enough to drink, prepare food and use for medical needs. (The other 15 gallons are for bathing, washing clothes and the like.) Water gets to the front in vulnerable, slow-moving truck convoys that require armed escorts, or it is pumped from local rivers, lakes or ponds and purified by heavy-duty filters.For the Army, the logistics of moving water limits how it can use troops. When soldiers are deployed in the field, it can easily take 40% of them to move water and other materials, often placing them in vulnerable positions.
The solution? A diesel engine that extracts water from its own exhaust:
The Humvees in the the demonstration program are, from the outside, indistinguishable from other military vehicles, except for a small water spigot behind the right rear wheel. Beneath the metal panels of the truck bed is a system of pipes and filters, which can collect water whenever the engine is running, at a rate of one gallon of water for every two gallons of fuel burned.In the combustion process, the oxygen in the air combines with the hydrogen in the fuel, producing water vapor and exhaust gases. Rather than going out the tailpipe, the gases are vented through a catalytic converter to bake off as many impurities as possible, then run through two heat exchangers, which extract heat and cause the water vapor to condense into the collection tank. “At this point, the water is — at best — gray in color,” says Gregg Newbold, general manager of Hamilton Sundstrand’s Army and Marine programs.
From there, the decidedly unappetizing-looking water moves to a series of six “treatment beds,” which consist of proprietary carbon filters developed by LexCarb. The first four filters strain out black gunk so that the water becomes amber. The final two filters remove remaining impurities, resulting in water that is as clean, or cleaner, than the tap water of many U.S. cities.
From there, the system adds a chlorine solution to kill bacteria and algae that might form post-purification and then deposits the water in a five-gallon tank. A spigot inside the cab of the vehicle dispenses water chilled by the air conditioner. “It has a slight chlorinated taste, but compared to how it started out, it’s quite good,” says Hamilton Sunstrand’s Mr. Newbold. In theory, the tank could function as a source of drinking water for a crew of, say, four people over the course of a day. (It isn’t intended to be the sole water source for an extended period.)