Who are "They" and what makes them so sure that you need 1" per week? Water as you need to maintain the turf at a level of lushness and green that satisfies you. That may be less than 1" and it may be more. You can manipulate the times that you run the system, during the water window that you have. Also if you don't know the precipitation rate of the sprinklers, (each zone may be different as are the rates for rotors and sprays) then you won't be able to set up the time to run. One of those useful pieces of information.