water is always world and uses specific water textures
now if you want to have moving water i.e. surface texture you can so do this instead
make box - no draw all sides, top side apply water - that box will then be the actual water
then make one box, all no draw, 1 unit above the water may even aligned or merged inside in your water box. make this a func_brush - non solid - on the top put on your moving texture and rotate it until the texture is going the way you want.
if you just want water with a current, make water box put pushzone in it
you're done