Minecraft wiki entry for Cocoa_bean_farming, associated text: This design exploits the fact that water will propagate infinitely so long as it flows downhill first, allowing a single water block and single piston to cover any width of wall. This is based on MinecraftMaximizer's design at the bottom of this page, but is considerably more space and material efficient, using a piston rather than a dispenser to release the water. This is because dispenser designs require 2 toggles: 1 to release the water and 1 to stop it; piston designs can work by a single button press. It does require more redstone than Maximizer's, which only uses 1 dust in the dispenser, with the advantage to this design being that it can be triggered from the ground.