Yeah, in Indonesia (and other parts of the world), the 5-gallon jug you would stick in e.g. a water cooler is called a "water gallon".
TIL! Not the first time I've made a mistake on account of failing to detect that a different English was being used.
I assume it's a local/informal unit of measure? DDG doesn't know what a "plastic gallon" unit is.
TIL! Not the first time I've made a mistake on account of failing to detect that a different English was being used.