"I have a promise to keep to the kids of India. After 'Paani', a film like 'Mr.India'. But not till 'Paani' is done," Kapur posted on Twitter.
"Paani" was written 15 years ago, and it is only now that Kapur has found a producer for it. The movie will be made under the Yash Raj Films banner.
Kapur says the wait was long because he wanted a producer "that clearly saw my vision of the film, loved it, and added to it".
"Found that in Aditya Chopra," he wrote, adding: "To me, a film must be larger than its story. Larger than its director. Larger than its actors. Larger even than its own vision. Always tried that."