I understand Colorado has similar draconian water-rights laws.
Regarding crying about constitutional rights concerning water, the states have never amended the Constitution to enumerate a right to water. So the gentleman in question is learning about unchecked 10th Amendment-protected state powers the hard way. Ciizens need to work with their state lawmakers to iron out old laws that possibly no longer serve a purpose.
In fact, a joke that I have heard about the northwest is the following. How do you know when it is summer in the northwest? The punchline is that the rain has gotten warmer.
I also understand that the northwest gets so much rain that its hydroelectric-generated power gives the northwest some of the lowest prices on electricity in the country.
So I'm not quite sure why Oregon is concerned about people collecting rainwater. On the other hand, why do people in northwest need to collect rainwater? I'm sure I'll get some insights from northwestern freepers on this issue.
Eastern Washington, eastern Oregon (which has deserts) and Idaho (also has deserts) are not blessed with heavy rainfall.
I suggest you look at an atlas of the three states.