/room/water_room may be used to simulate a room that is a water
surface or under water. It is inherited froom /room/room, and you have
too understand how that works in order to understand the rest of this
file.

A room inherited from /room/water_room may also be used as a normal
room. Whether it is waterfilled or not is controlled by using
properties: If the property "waterfilled" is set, the room's special
behaviour will be activated. This makes it possible to simulate tides,
airlocks, etc..

The things that are different when the room is waterfilled are: 
* Objects dropped will sink if there is a room defined for them to
  sink to.
* A room may be defined as being underwater and having another room 
  as its surface. Players without an air supply will be forced to 
  that surface after a set time.

Look at the file itself for more exact explanations on what functions 
are available and how they work.