Pooled Resources

Here's a quote from the infamous DwarfWiki.

Murky pools are small pools of water one Z-Level deep on the surface of the map. Dwarves with the fishing job active will attempt to fish in them. Murky pools can evaporate completely in summer in sufficiently hot climates, or can be drained manually, but in either case can be refilled by rainwater or melting snow or ice.

Drinking from a murky pool will give dwarves an unhappy thought. Dwarves will not normally drink from murky pools if they can at all help it; they will prefer to remain thirsty instead of drinking from a murky pool, holding out for the hope that well water or some alcohol will be produced in the mean time. However, if there are no other water sources that present themselves, dwarves will eventually force themselves to drink from a murky pool when they become very thirsty.

On reflection, I am very happy I no longer have to drink from murky pools.