|This article is about an older version of DF.|
Freezing of water
Water in Dwarf Fortress can freeze to become ice if the temperature is low enough and the water is exposed to the air. The tile must be tagged as 'Above Ground' in order for the temperature to get low enough, as all 'Subterranean' tiles remain at a consistent temperature of . However, inside glaciers even 'Subterranean' tiles appear to be cold enough to freeze water.
Water at level 1/7 freezes to become an ice floor. Water at level 2/7 or greater freezes to become an ice wall. Any ice wall will return 7/7 water when melted, or can be mined for 1 boulder of ice.
This may be useful if embarking on a location with limited water and seasonal freezing, as if collecting the spring melt-water. One could expand a lake to 3.5 times the original size (if 7/7 full) so it levels to 2/7, let it freeze then thaw, then drain the expansion to a deeper cistern. If the water in the original lake is preserved at 7/7, the process may be repeated each year.
Creatures on a water tile that freezes into an ice wall are instantly killed. Dwarves die with the message "<dwarf name> has been encased in ice". The ice wall must be melted or mined in order to regain the items/corpses. Note that due to a bug items that are in walls that melt will still be there, but will be invisible and unviewable except through the stocks screen. These items can be recovered if the tile ever becomes accessible again (through mining after the tile refreezes or by draining the water).
Floor hatches will disassemble if covered by an ice wall. The hatches and any associated mechanisms survive the process, but will wash away once the ice melts.
Ice can melt when the temperature rises as part of the natural cycle of seasons. Some biomes may be frozen all year round and others may never freeze. Ice can also be melted by proximity to magma. An ice tile with magma above or beneath it, or within 2 tiles on the same z-level, will cause the ice to melt (or will prevent water freezing in the first place).
One of the first challenges presented by a freezing climate is the lack of water in any conveniently drinkable form. Along with trees, water may be the hardest resource to obtain. The ice chunks left behind while digging through ice cannot be melted into drinking water. There are several ways to approach a freezing area. One of them is embarking with a volcano in site, utilizing the natural obsidian surrounding it to create magma-safe floodgates and mechanisms to effectively melt ice. Another is to penetrate to the cavern levels, which may have water in liquid form. Note that ice can be used to create buildings and workshops, which may be melted by magma or other heat sources, and constructions, which will never melt.
Remember that staying outside too long can cause your livestock and dwarves to die from exposure if the temperature is low enough, although clothes and armour may help to stave it off.
While channeling ice and magma, supervise your miners to ensure they are not encased in cooling magma or freezing ice.