As stated in the Development Regulations 2008, Schedule 1A (Development that does not require development plan consent):
Water tanks (above ground):
The construction or alteration of, or an addition to, a water tank (and any supporting structure), other than in a Historic Conservation Area, if—
(a) the tank is part of a roof drainage system; and
(b) the tank has a total floor area not exceeding 15 square metres; and
(c) the tank is located wholly above ground; and
(d) no part of the tank is higher than 4 metres above the natural surface of the ground; and
(e) no part of the tank will be in front of any part of the building line of the building to which it is ancillary; and
(f) in the case of a tank made of metal—the tank is pre-colour treated or painted in a non-reflective colour.
Water tanks (underground):
The construction or alteration of, or addition to, a water tank (and any associated pump) if—
(a) the tank is ancillary to a dwelling erected on the site; and
(b) the tank (and any associated pump) is located wholly below the level of the ground.
The above information is advisory only. It is intended to provide a guide and general understanding of the key point associated with the particular topic. It is not a substitute for reading the relevant legislation or the Development Plan.
It is recommended that if you are intending to undertaken development, you seek professional advice or contact the Council for any specific enquiries or for further assistance concerning the use and development of the land.