A leak is when there is a hole in the level, Or part of the level is outside in the void Imagine this:
Your level is a large water tank, And the water must stay in the level for the fish/Player to play in, If there is a leak, All the water escapes, Even if the leak is at the top of the map.
What can cause a leak?
Entities out side the map
holes in the skybox
Model Origins (The blue sphere)
Displacements DO NOT block up holes, Add a brush under it
some Entity brushes don’t block up the skybox, Be aware of this when using the Pointfile
How to identify a leak!
Water is white and looks terrible: http://filesmelt.com/dl/water1.PNG
Light settings can mess up
The skybox will break is certain areas
When the compile log says: LEAKED, Belive it or not, You have a leak
How to fix a leak
Click on the map tab and select “Load Point file”
OH MY GOD, A RED LINE IS ATTACKING MY MAP, AHHHHH
Simply select all the items that are around the red line and delete them
Plug up any holes and laugh:
LEAKS CANNOT HARM ME!!!
The red line will stick around until you compile or press “Unload Pointfile” in the map tab
Beware though, Just putting a new Box of sky around your map is a VERY poor way to fix the problem