r_novis
This variable toggles the use of VIS information from the map data. When this variable is set to "1" the game will calculate it's own VIS information on the fly instead of using the information stored in the map data, this will cause a severe performance penalty in the game. When "r_novis" is set to "1", the variable "gl_turbalpha" has a value lower than "1" and the server allows the client to display liquid transparently the player will be able to see through liquids. This is a nice effect to see but it is not recommended to keep this variable set to "1" because of the huge performance penalty. It is possible to enable transparent liquids and still keep this variable set to "0" (and thus not experience such a severe performance drop) by using maps that are VISed accordingly. You can visit the official Water VIS site at "http://www.sod.net/" and download the vispatch program along with the patch data files which you would use to update the VIS data for all of your game maps. There are also map packs available that contain VISed versions of the original ID maps.
Calculate VIS information for unVISed maps.
Do not calculate VIS information for unVISed maps.