My favorite response to a customer asking me how to water correctly was always, “Sir, if you lined up ten lawn guys and asked them how to water your lawn you just may get ten different answers.”  There has always been great confusion and many different theories when it comes to irrigating the lawn.  I imagine it stems not only from inexperience but also from incredible growth in the irrigation system installation business.  Many sprinkler system installers have given incorrect guidance when it comes to how to water a lawn.  After all they just installed a system that cost several thousand dollars and they want to make sure that their customer feels comfortable with the amount of money they spent.  Much to the dismay of many sprinkler guys, the lawn does NOT need to be watered every single day all day long nor will ten minutes per zone twice a day make a difference either.