I think the initiative has a couple of flaws that may doom it.  Solar panels should be allowed for 100% of the area.  They absorb a lot of energy as useful energy and reflect much of the other energy so reduce heat island effects.
A city is a large impervious area that does have a runoff problem but for a place that just got around to allow a rain barrel for houses with yards which is much less impervious space, the problem of downstream users not getting water should be considered.  Further rain will likely not be enough to supply most gardens even with storage so more water will be used by Denver.