An underground system can be either manually or automatically activated. With a manual system, you turn on the sprinklers by opening a water valve by hand each time you want to water.
Automatic systems use a timer.
Both systems are installed basically the same way. The valve is usually located directly outside the house, and can be connected to an existing outdoor faucet. Polyethylene plastic pipes are also used because plastic is easier to work with than metal, less expensive, and less likely to crack during a winter freeze. PVC is a rigid plastic and is the stronger of the two. It should always be used at the main water supply to the sprinkler system.