Did they have sterilisation tabs for water generally issued WWII or was it just take a chance on it, in WWI some of our boys got so thirsty they took water from shell holes.
In one of my books on that conflict a soldier was drinking the water he had just gathered from a rather large shell hole and a Germanicon corpse bobbed to the surface!!!

Though the 2 conflicts were streets apart they shared a common theme as far as I gathered from my readings on conflicts your mates were everything to you.
I should say that maxim holds true for todays soldier.