The document does a good job of making the case for encouraging rainwater harvesting and enacting regs that encourage it, while still ensuring that it's done properly to protect human health.
They start with a list of benefits from rainwater reuse including some that are pretty obvious and some not so obvious. Among the more obvious benefits are the fact that rainwater is a relatively inexpensive source of water (if you amortize the up front costs of installing the system), it reduces runoff (often a source of erosion and a non-point source of water pollution), and it can readily replace high quality drinking water used for outdoor watering and some indoor uses that don't require a potable water source. Two of their listed benefits I thought were less obvious: reducing seasonal peak demands and permitting greater demand management for drinking water systems. The first of those benefits might be limited in a place like Tucson where peak demand typically occurs at the beginning of summer, before the onset of our summer rains, when there has typically been no rain for 1 to 2 months and therefore the typical residential rainwater storage systems will be empty. But it could reduce demand during periods where the summer rains disappear for a week or two and the really hot weather returns. The second benefit could be very significant in places like Tucson, where a significant amount of household water use is for outdoor irrigation which can vary considerably depending on population growth, housing demands, weather, and a host of other factors. Per capita demand for essential household uses is pretty predictable, largely unresponsive to changes in price, and permits planning based almost solely on population numbers.
The one thing that really impressed me about the document is that they didn't simply discuss the ways that rainwater harvesting could be regulated and why it should be encouraged. There was also good discussion on how to create increased demand for inexpensive alternative sources of water for non-potable uses by increasing the amount people pay for water that is used to keep their grass green, for instance. Price is the most reliable driver for desired changes in behavior (my nod to Aguanomics) and serves to make alternatives economically attractive to those unlikely to change their ways out of a sense of community.
Here's what the document says on the subject (pp. 5-6):
The high rate of water consumption in the U.S. is coupled with water cost rates that are among the lowest.
Price, therefore, creates little incentive for conservation or the use of alternative sources.
And on pg. 9:
An increased price of potable water would encourge investment in rainwater harvesting systems because they offer a long-term inexpensive supply of water after the initial capital investment. The combined actions of establishing certain requirements for rainwater harvesting systems and increasing the currently underpriced cost of water creates a complementary system that can encourage the use of alternative water sources.
I really couldn't have said it better myself.