Dwayne, thank you for the detailed reply!
I've seen purple pipes used to carry recycled wastewater in California. Do you know if the stormwater needs to meet any water quality criteria before it's used for irrigation?
On No.4, why is it less of a problem if a stormwater irrigation system breaks vs. the treated water? Is it because something different is being irrigated, or because of the existing backup system?
Bart, thank you for replying.
The question came to my mind while driving by stormwater retention ponds in a new development, so urban and suburban environments were what I was thinking about. I was also thinking about stormwater that ends up in combined sewers. You are also right that the stormwater becomes a part of the hydrologic cycle, especially if it infiltrates into the groundwater or is released back to the receiving water.
I came across this article on the future Sites reservoir in California in May issue of the Civil Engineering Magazine. Is it something similar to what you had in mind when talking about collecting wet weather flows to supplement dry weather base flow?