Yes, the water laws prevent us from saving rain water for irrigation of our plants and gardens. You can read the full details at the Denver Water's website - but beware it is done in dreaded frames so you will have to search under conservation, FAQ, or read on for the actual link.
But to confirm, Denver residents cannot save rain water for watering of plants or gardens or anything. You CAN save your shower water, but not if it has touched you. You can stick a bucket in the shower to capture the water while you wait for it to heat up. You may only use water ONCE. It is the property of Colorado. NOT YOU.
This is just absurd to me. They give the following example: If 80,000 people saved 100 gallons.....YEAH RIGHT! How many people do you know that conserve like that? Ha! So anyway, read about not saving rain water. Now I must got take a shower and save the water in a bucket before it hits my skin.