func_water
1.Firstly, create a good sized room (300x300x300) and place your info_player_start and a light in there.
2.Next add a water brush
below the room.
NOTE: you may have to put the water brush in another empty room with light on its surface,
otherwise the water surface will be black. Apply the func_water entity to it.
Give it a
"targetname"
"water1"
"lip" "8"
"angle" "-1"
3.Place a trigger_once brush
in the room, so when the player walks across it it triggers the water. Give it a
"target"
"water1".