I am going to come at this from a different angle.
You are new to the system it is large.
It maybe that the valve is the valve can be manually tuned on and you are looking in the wrong place for the water.
It could be operating drip irrigation that would not be obvious to you where it is located on the property.
It could be operating bubblers for the trees that you may not see in operation.
It may be on the monument sign that is across the property.
It may be in an interior area of the church that has landscaping.
It may be in the islands in the parking lot with drip.
When a project is that large it is easy to miss a valve with out the history.
It may be on the auto fill to a fountain.
Good Luck.
Dan