So in this file:
oxide/data/StackSizeController_vanilla-defaults.json

It allowes water to be stacked up to 2147483647 for regular water and salt water.

Players exploit this by having two water jugs and moving water from one jug to the other. 

This is not vanilla default. I've tried changing it to 5.000 (I know that would mess up the car tanks), but the plugin wont allow me to do so, it just download the default config with the exploit again.

The water has always stacked that high since the plugin release, and as it is not an item that can be used to attack other players i can see no problem with that . i personnaly never carry water as i find that there are enough berries to sustain health ,

Careful, over hydration kills.

Talk about drinking yourself to death  :)