The liquid state, which behaves in the game just like it does in reality. In this state, the substance is constantly changing shape, trying to fill a given place to a degree which depends on the amount of the substance. Unlike gases, it does not expand to the whole room. It always falls down to the floor. If some gas appears in the liquid or below it, it will rise to the surface.
Duplicates can walk on the bottom of the tanks, but they must have access first, e.g. a ladder. You can build this without any obstacles. You can also designate the construction of machines or pumps, or put up new walls and thus divide the tank. If the liquid in an affected field exceeds 1/3 of the volume, the objects in that area will stop working. Duplicates will have to first get rid of the liquid, in order to use the equipment.
In the game, no liquid behaves exactly as it does in reality. Things are a little more flexible and rubbery, due to the one field - one type of material/substance principle. In caves that are full of water, you will see bubbles of some gas, instead of thin layers just under the ceiling. Also, when it goes down slopes, the liquid first takes the form of a small bubble, and then it slides down. Any liquid can be converted to the gaseous or solid state if the appropriate temperature is obtained. Liquids can destroy thin walls, both natural and artificially constructed, if the amount of a given liquid is very large or if the density of it is much greater.
Water. The most important liquid and resource in the game. You can find it in natural caves near the starting location. It achieves a density of about 1000kg per field. You will use it in many branches of colony life, e.g. in order to produce oxygen or food, although the duplicates do not drink water nor do they directly need any other liquid to consume.
Polluted (or Contaminated) Water. It has the same properties as pure water with one crucial difference, that it cannot be used in production, industry or hygiene related systems. Additionally, it emits contaminated oxygen. It occurs in large quantities in the toxic biome. It is also appears as a side effect, when your duplicates do not get to the outhouse or vomit as a result of stress. It is also a waste generated during production or e.g. by the shower. It can be purified back to its clean form.
Magma. This is a unique substance, it is a rather hot mixture of various minerals and substances. It has an unusually high temperature, that melts other rocks and condenses liquids into their gaseous states, e.g. water into steam. Most often, however, it will turn into igneous rock under the influence of ambient temperatures being lower than its own.