I heard a story from a Chinese tourguide. According to the story, Deng said that by the letter of the contract (and it was a forced one at that), the UK could hold Hong Kong in perpetuity. Then he said, “Do you know what ‘Hong Kong’ means in Chinese?” “It means fragrant harbor.” “We have no contract specifying that we supply fresh water or other utilities to Hong Kong. How long do you think it will stay fragrant.”
Just a story I heard.
Most post-hostility treaties benefit one country at the expense of another. China has grabbed huge chunks of land from its neighbors after beating them in battle.
The water theory doesn't hold water. Countries without fresh water have been figuring out how to supply themselves since forever. The principal problem relates to agriculture, which requires huge amounts of essentially free water. Singapore used to rely on Malaysia for cheap water. It has now weaned itself off. The Gulf emirates have never had cheap water, but they have somehow made do.