Rainwater harvesting

(dislamer: I am an architect, not a civil engineer. So I only have a basic understand of stormwater management). The v4 language refers to replicating natural hydrology. Which, in my mind, is very different from v2009 that requires reduction in quantity and increase in quality. My thought was that by collecting rainwater, say for toilet flushing, one would be reducing the amount of water that might naturally infiltrate into the ground; and thus, prevent the restoration of natural hydrology. We have a project in maryland where we actually could not capture as much rainwater as we would have liked, because code dictated a certain amount of stormwater must be allowed to infilrate and runoff, as it would on a natural site.