With the massive wildfires in our recent past, you can't deny that California is one drought-ridden state where every ounce of rainwater is vital. So, you'd think they'd have rainwater harvesting completely banned, right? Wrong.
In 2012, the state passed Assembly Bill 1750, which allowed the Rainwater Capture Act of 2012. Basically, it made collecting rainwater legal so long as you follow the California State Water Resource Board's requirements.
The bill outlines that certified landscape contractors can install water collection systems "used exclusively for landscape irrigation or as a water supply for a fountain, pond, or similar decorative feature in a landscaping project." Similarly, the bill struck down landowners needing to have water right permits to collect rainwater from rooftops.
In some counties, there may even be incentives for rainwater harvesting. Check with your county for more information.