40d:Flood

Flooding generally refers to water getting loose and spreading out over an area, usually in an unregulated fashion. While this can be useful in creating plots of muddy ground for farming, deliberately setting any amount of water loose in an area is risky at best, and at worst, will result in lots of fun.

As in real life, water will seek to spread out given open space. In Dwarf Fortress, this means that water will spread until all tiles achieve a depth of 1/7, or it fills the space it is enclosed in. Water at a depth of 1/7 will eventually evaporate, leaving behind a muddy floor. Because of this, it would be nearly impossible to ruin a fortress with water from finite sources such as a murky pool. Note, however, that rivers, brooks, and oceans are considered to have offscreen water sources; their supply has been observed to be infinite, as has that of aquifers. Tapping into one of these without some means of regulating the flow is almost certain to result in fun.

Water movement is a major source of lag in the game.

Flood speed is counterintuitive. For example, if you build a ramp beneath the bottom of an underground pool connected to a large drainage shaft leading to a chasm, all the water in the upper levels of the pool will drain down into the drainage shaft leading all the way out into the chasm, filling it all nearly instantly 7/7 with water and submerging your hapless dorfs however far away in the shaft they may be. But once the space is filled, the flood slows down to the glacial pace at which water usually moves down tunnels, giving them plenty of time to drown.