If it was his graphics card, I would suggest that he update his drivers, but I actually doubt its his graphics card, seeing how this is the only game affected (unless the specific driver he has says that the water in CSS has the missing texture affect, aka purple+black squares).
But yea that's pretty odd even after reinstall. Did you do a clean reinstall? Delete CSS off steam, THEN navigate to your steam folder in program files>steamapps>username>then delete counter strike source. After that redownload from steam/install CSS.