Abstract: A drip irrigation unit with air-controlled siphon flow. A tank holds a quantity of water for slow distribution. A siphon carries that water from the tank to a pan. Siphon flow from the tank to the pan is controlled by a cover that prevents air from filling the space evacuated by water flowing from the tank. A vent hole normally covered by water in the pan allows air to intermittently enter the cover to relieve the slight partial vacuum inside the cover. When the cover vents, water again flows through the siphon to the pan until the vent hole is submerged and the air pressure sufficiently drops inside the cover. Alternatively, a cap and vent tube may substitute for the cover and vent hole, respectively. A displacement element may be incorporated into either the cover or the cap to start the siphon flow by raising the water level above the siphon.