trying to add water to a map I'm making and it turns red after compiling and building the fast file when I load it in the game.

Image shows what I'm seeing and using in the editor.

water from your tools is for effect only not texture
use a liquid from you texture usage
and its red because you need to put one or more reflection probes in your map ,right click your mouse in radiant and you will see reflection_probe select it and put it over your water say 8' in the middle of your lake and maybe one in front of your building's not to many ,not close to another probe you do not need to give them angles, most maps only need 15 to 30 on a finished map you should only need 2 or 3 for now to get rid of the red water and rainbow effect on your guns

Thank that worked.

glad i could help