Random Thought on Density and Water Runoff

I just randomly had a thought a couple of days ago: couldn't, potentially, urbanization allow for a decrease in the amount of water wasted as runoff?

Yes, urban buildings, especially as built currently, greatly reduce the amount of water allowed to recharge into underground aquifers; this water instead ends up on rooftops to evaporate, or runs off pavement, directly into streams and watercourses, maybe even causing preventable erosion. Suburban environments, those that emphasize the automobile, with large streets, and parking lots everywhere, are very bad, too.

But what if all urban buildings, or even just a majority of them, were built with "green roofs"? This could enhance the position of the urban, denser environment in respect to the suburban, as all building roofs could potentially replace at least part of the water collection role that the ground those buildings cover played, whereas suburban "sprawl" seems doomed to waste water away. I cannot see any way for parking lots to be "greened up" like roofs can, as cars still need to drive across them; is there any way to do so?

Just a thought.