I just visited my brother Ely in Glendale and the forecast was calling for rain in the next couple days. He was happy about that. They need the water. Glendale gets an average of 21.09 inches of rain a year (according to Wikipedia) and had only 16.95 inches in the last ten months (according to Weather Underground). Ely just emailed me that a meteorologist on the radio today said they’ve only gotten 5.15 inches so far this year, 9 inches below average).
But what is going to happen to that rain water? Almost all of it will fall on rooftops, sidewalks, parking lots and roads:
For a case study, I looked at Ely’s neighbor’s roof. They have a gutter on the low side, which will catch most of the rain that falls on that roof:

The neighbor’s gutter dumps into a drain pipe that heads towards the street on Ely’s side of the wall, picking up the runoff from another roof along the way.
The system moves the water that lands on Glendale to the ocean quickly and efficiently. Meanwhile, they wash their cars and water their lawns with water pumped in from the distant Colorado River.
Here’s a totally different way of thinking about rainwater, from another, drier city that also relies on the Colorado River–Tucson, Arizona. Watch for the wow moment, starting around 1:20:
May 6, 2013 at 10:19 pm
Awesome. Also, it heartily pisses me off that a city that gets more rainfall in a year then the amount of water they need, throws that water away and imports water from the Colorado river. I live at the very upper end of that watershed. I need water for irrigating my pasture and all to often it isn’t available for use because downstream users (Like Tuscon) have senior water rights for it. While they are throwing out their own home’grown’ water. I’m VERY glad to see some changes taking place about that!