Throughout the Earth series, several forms of rescources appear.
In Earth 2150, only one form of material is seen in-game. These rescources are marked by "blinking spots" on the ground.
Other forms of material such as wood or water are seen in several of the missions and maps, but the player cannot "mine" these.
In Earth 2160, three diffirent forms of material are featured. The Aliens are the only faction which requires all three, the other three factions only need two of the three.
Water is needed by the ED and the LC. It usually appears in frozen form; only in a handful of missions (mostly those on Eden) does it appear in liquid form, and even then it cannot be mined (with one or two exeptions).