In Texas we have "the right of capture". this opens up a big can of worms...especially here in s.a. you know that saying....." whiskey is for drinkin, and water is for fighting"
This is half true, at best.
Rule of Capture only applies to groundwater, and even that can be limited especially if you're over the Ogallala, or Edwards/Trinity systems. Generally, underground water belongs to the landowner, but that right can be limited if the well is wasting water, (malicious/wantonly negligent use or excessive runoff) contaminating the source, or causing undue damage to the surface estate due to overdrawing causing the land to subside.
Now, surface water presumptively belongs to Texas, so the State has free-reign to regulate. However, it only becomes "surface water" once it reaches either a recognized waterway/water source such as a stream, river or lake. On its journey to the lake, river or whatever, and is crossing over the land of someone, it doesn't belong to the person but it can be captured. (It's
ferae naturae so to speak.) However, the capturing party cannot substantially interfere with the course or natural flow of the water.
This includes diverting the water to capture it. So, I would say under a literal reading of the law, that rain barrels, and especially the drainage/gutter system used to divert the rain to the barrels, is not within the spirit of the law. I know a lot of people who capture rain water to use in their gardens, etc., but water is so damn precious in this State, I can actually understand the need and want to regulate, or else it could get out of hand and cause a nightmare for the river and lake systems due to increasingly diverted rain paths and what not.