In determining the amount of compensation under this section, regard shall be had to the diminution in the market value, at the time of awarding compensation of the property in respect of which compensation is claimed; and, where such market value is not ascertainable, the amount shall be reckoned at twelve times the amount of the diminution of the annual net profits of such property, caused by the exercise of the powers conferred by this Act. No right to any such supply of water as is referred to in clauses (d), (e) or (f) of this section in respect of a work or channel not in use at the date of the notification shall be acquired as against the Government, except by grant or under the Limitation Act, 1908, Part IV.