When water power, created or reserved in any manner by works wholly located in the same town in which it is appropriated and used, is used by its owner, the whole shall be assessed and set in the list as incidental to the machinery which is operated by it, and not separately as distinct property. When such power or any part thereof is leased from its owner, it shall, to the extent to which it is so leased, be assessed and set in his list at a valuation not exceeding one hundred-sevenths of the net revenue derived therefrom.