Standard Water & Sky - from The QuakeLab

The QuakeLab - http://www.in2nett.com/stevefu/QuakeLab

TEXTURES:

        Your choice of: WATER0, WATER1, WATER2, or WATER3 and SKY1/SKY4

ENTITIES:

        NONE

WHAT TO DO:

        Make a simple six-brush room (ie: a box.) Expand the floor brush
        downwards. The deeper you want the water to be, the further down
        this brush should be extended. Texture this floor brush on all sides
        with any water texture. Copy the water brush - the copy will be the
        ground. The top face of the ground brush should meet the bottom face
        of the water brush, or they should overlap a bit - this is to avoid
        leaks. There will be a leak in the level if water brushes are not
        separated from the void by non-water and non-sky brushes. Sky brushes
        do not need any such treatment. Now lower the bottoms of all four
        walls so that they cover up the sides of the water brush. Now the
        level has no leaks. Texture the ceiling brush with a SKY1 or SKY4
        texture.

OPTIONS:

        You can make shapes in midair that are made of water - they can be
        passed through by the player. Water blocks floating in midair,
        etc... Why? Why not?