Section 23(1)(a) in The Chennai Metropolitan Water Supply and Sewerage Board's Water Tax and Sewerage Tax (Levy and Collection) Regulations, 1991
(a)If any building in the [Chennai] [Substituted for the word 'Madras' by the City of Madras (Alteration of Name) Act, 1996 (Tamil Nadu Act 28 of 1996).] Metropolitan Area is constructed or reconstructed the owner shall give notice thereof to the authorised authority within fifteen days from the date of completion or occupation of the building, whichever is earlier.