OpenValve is an open-source alternative to classic irrigation timers. Instead of watering on a fixed schedule, it measures soil moisture and opens when the soil becomes drier than a configurable threshold. OpenValve is suitalbe for little greenhouses, balconies, plant beds, community gardens and off-grid irrigation setups. At its core is a 3D-printable, bistable pinch valve that consumes power only while switching. It works with gravity-fed water sources as well as pressurized systems up to 4 bar, tolerates particle-rich water, and runs for approximately three months on a 9 V battery. The mechanical design, electronics, PCB, bill of materials, and software are open source, allowing OpenValve to be repaired, modified, or adapted for other sensor-controlled liquid-handling projects.