Apparently it is in 3 states, but thankfully ignorance is losing this one.

"...that rain belongs to someone else."

Collecting rainwater now illegal in many states as Big Government claims ownership over our water

So, let's buck the system...a little personal activism never hurt, especially if you live in Washington, Utah or Colorado.

Here's a couple of good how-tos:

Build A Rainwater Collection System on Wikihow.

And...

That does seem a bit of a strange reaction to drought. Here when the drought started to bite the various goverments in the affected areas started to subsidise purchase of rainwater tanks. Of course the last couple of years the problem has been floods and how to get rid of all the excess water. The droughts will return though but more people should be better prepared for them.

It's been illegal in Colorado for quite a while and it's not so much because of big government but water rights that go way way back. Water rights are really complicated around here. The laws are slowly changing and some areas can now legally collect rain water.
And, while it technically is illegal, nobody has ever been prosecuted despite all the rain water collection barrels around here.
I've got three barrels set up and am planning more. The theory behind the laws is that the rain water going down my downspouts is going to go way way down to the aquifer or travel all the way to an irrigation ditch and somehow my moving that water from the downspout area to my gardens is going to somehow affect this.

At first, I was astonished, amazed and disgusted to hear that WA had any laws against collecting rainwater. It took me 2-3 years to dig enough ditches to get the darn constant rain to run off, away from my beds!

Then I realized "dry, inland WA" is nothing like "wet, coastal WA". OK, people living in a desert might get wierd about water.

But what could they do with collected water, that would keep it from eventually going wherever it was going before they (briefly) diverted it?

So now I'm just astonished and amazed.

But I am glad that ATP now has a Permaculture forum. Thanks, Chris and Dave!

Hey Rick...

When I think of rain water collection, I'm thinking that in most instances it's from the roof via gutter into barrels for later use. However, other uses of rainwater are through diversion on the ground by way of trenches to the base of trees and into beds, swales which are small dams that both collect rainwater into organic material such as dead wood and mulch, as well as divert it into a holding area like a pond, pool, or reservoir.

Well, I have such a small yard (square yards, not fractional acres) that I have trouble imagining constructing a dam and a reservoir.

But I can see where that COULD divert enough water from a river, for use in later seasons, that the resulting absorption & evaporation or transpiration made a difference down-stream.

I wish we could divert some of the runoff from WA to CO or CA!