I've got a shallow well and I'm about 2 miles from a big uninhabited lake. Even so, rain catchment is a good idea, if nothing else, to better control where the water goes on the property, and when it goes there. Instead of it all accumulating around the structures off the roof, it can be directed and dispersed more evenly around the property at a dryer time when it is needed. We seem to give so little thought to water these days.