Section 62(4) in West Bengal Municipal (Building) Rules, 2007
(4)Every bathroom or water closet shall(a)be so situated that at least one of its walls shall open to an interior open space or exterior open space or shaft and shall have an opening in the form of window or ventilator or louvre not less than 0.40 sq. metre in area;(b)not be directly over any room, other than a latrine or water closet or a washing place or a bathroom or a terrace, unless it has a water tight floor;(c)have the platform or seat made of water tight non-absorbent materials;(d)be enclosed by walls or partitions and the surface of every such wall or partition shall be finished with a smooth impervious material to a height of not less than 1 metre above the floor of such a room;(e)be provided with a door completely closing the entrance to it; and(f)be provided with an impervious floor covering sloping towards any drain with a suitable grade and not towards any verandah or other MOM.
