The issue here isn't physically exporting the water but exporting the externality. It's like investing in a heavily polluting industry is "exporting pollution" - the product itself contains trace of the pollution, but the local damage was done on behalf of the product.

I mean, once used this water ain't getting back to the aquifer anytime soon! If it were, we wouldn't be talking about aquifer depletion and there wouldn't be any concern regarding its use.

https://en.wikipedia.org/wiki/Overdrafting