Minecraft wiki entry for Water_gate, associated text: To create a water gate, the first thing to do is to create the channel. This can be done by digging it out of the ground or by placing walls on the ground. The gate is simply two pistons facing into the channel that, when extended, occupy the channel and prevent water from flowing. Sticky pistons with an additional block stuck to them can be used for wider channels. Also, for a channel only 1-block wide, just one piston will work fine. The pistons are then wired to a redstone signal that controls when they are on or off. The signal is commonly a lever, so that when it is on the pistons extend, and when it is off they retract.