CURRENT is a Single Player level. There is no in-game name for this level, nor is there any name included with the documentation. The level therefore is named after the filename.
While intended to include an ambient sound for the Water, Dave Weiden couldn't get the sound to loop.
This level is nearly identical to WATER1, which is nearly identical to WATER2. CURRENT showcases the Water having a current, thereby pushing the player along. The player can fight against it, especially if they jump or move to the sides of the Water brush, but otherwise will get pushed along with the current at a gentle rate.
This level had no .BSP file made for it, the player would need to compile the level out, because the level designer found that there was one bug that was too annoying for public use. Due to how Quake's engine works, the game automatically assumes that anything that pushes the player must be a Wind Tunnel and thus applies the Wind Tunnel movement sound to the brushes. This means that the player will hear said sound constantly.
A player wishing to work around the issue can delete the sound from the trigger_push entity in QuakeC.
Walkthrough
Walk forward to drop into the Water. Let the Water push you to the wall.