Water comes in several forms:
- as a potion of water
- in a fountain
- in a sink
- in a pool or moat
- in a rust trap, which somehow affects only worn armor, wielded iron, and wielded scrolls
- on the Plane of Water
Some monsters are made of water, for example:
However, they do not cause items rust.
Water is that clear liquid that you probably know from real life. In NetHack, water can rust objects or drown you, among other things. In a fountain or as a potion of holy water or unholy water, water has more magical effects. In a sink, water tends to be polluted, and it can have bizarre effects; for example, it might mutate (polymorph) you when you drink it.