Water is way easier. Could turn water into a working market in 6 months, given the political support. Water is something that is much easier to control. In fact, it's already controlled. All you need to do is limit supply (via mostly government "owned" resources) to whatever you deem to be a reasonable level, & charge for consumption. The smaller players (people with dams on their land) will follow.

You could even have the government manipulate prices by literally 'flooding' the market when necessary.

"Makes you wonder if there are carbon credits in other areas."

Sulfur Dioxide and catch shares for fisherman.