A correctly tuned sprinkler system can actually save water if it intelligently shuts itself on and off based on current conditions and forecast weather. The Sprinkler Switch loads forecasted weather information from NOAA and parses previously recorded data to determine if the sprinkler system should run or not.
At least that's the goal.
Currently the system fetches the forecast data from NOAA, visualizes the data on a dashboard, and allows Raspberry Pi GPIO to switch the irrigation controller on or off as an expansion sensor module. This is available over a Web interface, allowing the irrigation system to be controlled remotely.
The SprinklerSwitch project has FINALLY been updated to support the latest version of Raspian. The biggest hiccup was switching to the WiringPi2 library - which is now the defacto library for addressing GPIO pins. The good thing is pin addressing is now entirely in userspace (no sudo required!), however there were significant changes that required refactoring.
Things are up & tested with the latest version of Raspian however - so have at it!
First, construct a switch for your Raspberry Pi GPIO pins. I generally use MOSFETs for these low-voltage operations, with the gate to a GPIO pin.
Some sprinkler systems have a moisture / rain sensor that open or close a circuit to disable or enable the next scheduled irrigation. Usually if a sensor is not installed, there's a jumper wire to keep the circuit open. Replace the jumper or sensor wires with the open & ground wires on the relay or MOSTFET wired to the Pi. --> DO NOT WIRE THE GPIO PIN TO YOUR SPRINKLER SYSTEM <--. You'll likely frizzle-fry the whole thing. You want to close the circuit, not send any amperage to it. Seriously. Don't move on unless you understand your irrigation system. SERIOUSLY.
If necessary, enable the sensor or disable the sensor bypass on the irrigation controller.