Control the flow of fluid using the flow of electrons! This liquid valve would make a great addition to your robotic gardening project. There are two 1/2" (Nominal non-taped National Pipe) outlets. Normally, the valve is closed. When 12VDC is applied to the two terminals, the valve opens and water can push through. The valve has a gasket arrangement inside, so there is a minimum pressure requirement of 0.02 Mpa (3 PSI). Also, liquid can only flow one direction.

Plastic Water Solenoid Valve