Flooding

Flooding is a building status in Oxygen Not Included that occurs when a building is occupied by a tile of substantial liquid. A building becomes flooded if, during normal play, a liquid tile with enough mass fills its space, and it can also load into that state when a save is opened and the building is submerged in substantial liquid. Once flooded, the building remains so until the liquid is removed enough for the status to clear, or the building is demolished and rebuilt.

A liquid tile is considered substantial when it has at least 35% of that liquid’s maximum tile mass. For example, water becomes substantial at 350 kg or more in a tile. If a building is submerged only in an insubstantial amount of liquid, it is not considered flooded. On loading a save, a building that is submerged in insubstantial liquid can even lose its flooded status, while in ordinary gameplay it usually takes complete removal of the liquid to clear it, though sometimes the final few drops must be mopped up first.

Not every building can flood. Many utility and infrastructure buildings are immune, including liquid pumps, storage buildings, shipping buildings, sensors, switches, automation components, and several special-purpose buildings such as the Thermo Aquatuner, Farm Tile, Algae Terrarium, Tasteful Memorial, Water Cooler, Desalinator, Canister Filler, and Canister Emptier. Decorative items that only provide decor, and most rocketry components, are also immune, with Gantry and the two telescopes being exceptions.

Some buildings can survive in liquid without actually becoming flooded, which makes them useful in wet environments. Submerged Atmo Sensors always read 0 g, which can make them send a green signal if their threshold is set below that value. Critter Feeders do flood, but they can still function with only a thin layer of liquid around them, which is also useful for preventing off-gassing. For farming, Thimble Reed is the only plant that can grow fully submerged, while Waterweed is especially sensitive to being underwater and will report as too wet once the liquid level passes its limit.

Flooding is closely related to tile mass and liquid behavior, so it is often more about the amount of liquid in a tile than whether that liquid is present at all. This also means that certain edge cases can behave differently after loading a save than they do during active play. In practice, the safest way to clear a flooded building is to remove the liquid completely, then rebuild the structure if the status does not reset on its own.