Is It Illegal To Collect Rainwater?
In almost every state, no. Colorado caps it, a few states regulate it, and the rest leave you alone. Here is what your state says.
Collecting rain off your own roof is legal in every state. Colorado limits a household to two barrels and 110 gallons, Utah requires registration above a threshold, and a handful of western states attach conditions tied to water rights. Nowhere in the country is a rain barrel on a house a crime.
This is a scaffold sample, not finished editorial. It exists so the route, the layout, the schema and the link registry can be checked end to end. The real article is written in session S4.
Where the myth came from
Western water law assigns rain to downstream rights holders before it falls. That principle is real, it is old, and it has almost never been applied to a barrel under a downspout.
What people get wrong
Your homeowners association is far more likely to stop you than your state is. Several states passed laws limiting what an association can ban, and the rest leave the covenant you signed in force.