Hey, so, I originally posted this in the Terribe Suggestions Thread, because I wasn't sure if this counts as terrible, but here we go:
I think it'd be kinda cool if water sources would be more finite, and more essential to civilizations. For example, a fireplace in houses to melt the water during winter, and/or an option to eat ice, but with a risk of hypothermia if done repeatedly.
Also, if you dam a river in your embark, it should affect the settlements downstream, perhaps escalating into a war/peasant mobs, also its water should be able to be tainted/poisoned as a way of weakening the enemy settlement. Or maybe somebody/something accidentally dies and rots in the/next to the water in the middle of nowhere, which could cause minor problems to you, if the creature wasn't very big. This could be avoided with drinking booze/boiling the water before usage.
But water should also be able to be transported with a reasonable price, just like booze and extracts. Perhaps the price should go up, depending on the climate, and purity of water. Most expensive type should be distilled water, which could be usable by scholars, or in hospitals.
Settlements in scorching climates should be abandoned sometimes for lack of water, or they could attack/rob merchant caravans/other settlements for water, perhaps even securing and defending a location with a water source.