You will need a solenoid to control the water flow electrically, a timer to control the solenoid's power supply (24VAC, likely), the power supply, and the proper fittings to adapt the solenoid to your plumbing. The solenoid must be able to withstand the resting pressure of your line.
You can use a standard sprinkler valve to do this. It's not pretty, but it works. This is a good "annoy the plumbing guy at Home Depot" project. He may actually enjoy it, though.