Some of the members of the 300th received specialized training in the critical role of building and maintaining water purification systems at each new bivouac site. Sgt. Donald Ross led one of these units. (His daughter, Jan Ross, is co-author of this site.) These units supplied water not only for the 300th but for other divisions and civilians in the vicinity.

The First Army landed in France in a region devoid of potable water. The combat engineers constructed water holding tanks, purifiers, showers, latrines along with piping and plumbing to supply the needs of mess halls, field hospitals, repair shops, laundries and water stations for troops and vehicles. According to National Geographic magazine's November, 1942 article "QM, The Fighting Shopkeeper" water was extremely vital: "Fighting men drink up to three quarts a day." Quartermasters worked with the engineers by bringing in the cement, pipes, tanks and pumps they needed to construct the water systems. Water was also used to combat lice, bedbugs, fleas and disease through the use of steaming sterilizers.

Troop water needs in wartime greatly surpassed available quantities and additional water had to be shipped in. According to Ernie Pyle's "2nd Front Articles" about combat engineers, ships brought thousands of gallons in large tanks as well as 5-gallon cans. From that point, the duty fell on the engineers to transport the water to the troops. It was not uncommon for them to search for water deep into territory only recently evacuated by the enemy searching for water sources.

A combat engineer battalion usually carried enough equipment to set up four water points; two forward of the advancing infantry; artillery or armored units and one or two behind. As troops advanced, the behind water points would leapfrog ahead establishing the next forward points.

The first step in activating a water point was to locate a stream, well, pond or spring. In some cases, the source was enhanced by explosives creating a crater resulting in a water source called a sump from which the water would be pumped. The next step was to test for potability, turbidity and poisons. An engineer water specialist carried test tubes for this evaluation.

In some cases, the systems used for WWI were again used in WWII. They included sand filtration and chlorination. For most of the European campaign of WWII, the new ERDLator system was used. This system was named after the Engineering Research and Development Laboratory at Fort Belvoir, VA. (Fort Belvoir was where Donald Ross trained. His primary responsibility in the 300th in Europe was establishing water points.)

The ERDLator was a mobile water treatment unit that combined coagulation, flocculation, sedimentation, diatomaceous earth filtrations and hypochlorite disinfection. It became the principal water treatment employed in WWII and was later used in both the Korean and Vietnam Wars. It provided safe drinking water for both the troops and the civilians of liberated cities as the Allies moved across Europe into Germany.

Potable water usage by troops in combat was estimated by the military (on a per day basis in gallons) as follows:
drinking: 5
hygiene: 2.7
centralized showers: 1.3
food preparation: 3
vehicles: 3
heat treatment (ice): 1
hospitals: 65 gallons per bed per day
laundry (6 pounds per man per week): 2
construction: 1.5
Total use = 20 gallons of water per day per man.