Oil and gas operations don't just produce hydrocarbons. They also produce water. Lots of it. U.S. exploration and production generates over 25 billion barrels of produced water each year. Produced water was long considered a waste liability that had to be hauled off and disposed. But thanks to technological advances, operators can now treat, recycle and reuse it. Once an albatross, produced water can now be a revenue source. And with potential income comes a renewed focus on who owns it.