Yes, it's true. And interestingly, there are wells in Ireland, Scotland & elsewhere which have been tested & found rich in lithium. People would bring their "mad" friends & relatives to drink of the water or bathe in it. The effects would last for days or weeks. I read a book about this but here is a link that might interest you.

Gleann na nGealt | Fáilte Romhat (Welcome) to West Kerry