If you are looking for a good source of water supply, well…

Dwarf Fortress introduced us to dwarves drinking a lot of alcohol. They get too upset when they don't get enough booze to fuel them for a long time. But there are indeed certain times when they run out of alcohol supplies. What is left for them to drink is water.

In emergencies like running out of alcohol supplies, the only thing you can do to give them liquid to hydrate them is by building a well.

Well is one of the buildings needed for your entire fortress. Unlike other bodies of water such as rivers and lakes, water from the well does not freeze during the winter unless it is improperly constructed.