The troops can now get clean water, on demand, by zapping it with a handheld device. The SteriPen uses ultraviolet light to kill all microbes in water. The battery powered device weighs 4.5 ounces (189g) and is 7.3 inches (18.6cm) long. It takes 48 seconds to clean half a liter (16 ounces) of water (and 90 seconds for a liter). Just stick the probe in the water, press the button and watch the countdown timer. One set of batteries will purify 58 liters (14.3 gallons). Unlike purification tablets, the SteriPen method does not leave a chemical taste. For this reason, many troops buy a SteriPen, which cost a hundred dollars.
A lot of the weight of supplies shipped to troops in the combat zone is water. A liter of water weighs a kilogram (2.2 pounds), and in a combat zone, you need an average of 30 liters a day per soldier (for all uses). In areas where there is not yet purification gear installed, clean water has to be shipped in. That takes a lot of effort. Troops out on patrol have to carry water with them, even if there's a lot of water around, because the local stuff is, or may be, contaminated. For that reason, the military has portable water purification equipment, which is moved into combat zones as quickly as possible, to eliminate the need to ship in water.