Lawn Irrigation System:

You may have a lawn irrigation system.  You will need a vacuum breaker backflow preventer to protect against lawn and pesticide chemicals from being drawn in from your lawn and back into the water supply.  On a large number of lawn sprinkler installations the sprinkler head is below the ground level.  Water which may have been in contact with fertilizers and weed killers can then be back siphoned through a leaky valve in to the potable water system.  The two types of acceptable backflow preventers are the pressure vacuum breaker (pvb) or the reduced pressure zone (rpz).