DayZ field wiki · Survive
Canteen
A bottle with a strap
Short answer
A canteen is a water plan. Hands work until you find one. Empty is a warning.
Also: flask · water canteen
How it works
Canteens, bottles, and pots move water. Fill at a well, not a puddle. A second bottle is a kindness to the duo.
What to do
Fill when you see a pump. Don't walk inland dry.
Don't
Don't leave it empty as a joke.