Irish Water submits plans for €80m Stillorgan reservoir

Plans for an €80 million redevelopment of the 150-year-old Stillorgan reservoir, which provides drinking water for 200,000 people across south Dublin, have been submitted to Dún Laoghaire-Rathdown County Council by Irish Water.

Currently, drinking water for the southside is processed mainly at the State’s largest water-treatment plant at Ballymore Eustace in Co Kildare, before being piped to Stillorgan.

However, after having undergone expensive treatment at Ballymore Eustace to ensure it is fit for human consumption, the water then sits in the open air in three large reservoirs in Stillorgan before being piped into homes.

The water in the reservoirs is treated with chlorine and ultraviolet light before it is sent to homes, which reduces the risk of contaminants entering the system, but this is no longer considered an acceptable solution, Geoff O’Sullivan, head of major projects at Irish Water said.

“This is one of the last remaining open reservoirs of its size in Europe and leaving treated drinking water exposed to the environment is now considered an unacceptable contamination risk,” he said.

“Using the chlorine and the UV boost is considered a safe method of providing drinkable water, and it does undergo laboratory tests to ensure it is safe, but it is not considered a sustainable way of treating water.”

Covered reservoir

Irish Water wants to build a new covered reservoir, which it hopes to have constructed by 2020.

The utility does not plan to put a roof on any of the existing three reservoirs, but instead proposes to drain the largest of the three, known as the Gray Reservoir, for the project.

It will then construct the new covered facility within about half the area of the Gray Reservoir.

Once the new covered reservoir is operational, the two other reservoirs, the Upper Reservoir and the Lower Reservoir, will be drained and decommissioned and then landscaped.

“The two decommissioned reservoir areas will be maintained by Irish Water for future water infrastructure development to ensure that the community continues to have a safe, sustainable water supply for the future,” Mr O’Sullivan said.

The new reservoir will provide sufficient water for the existing population and to cover population growth up to 2031, Irish Water said.

The company said the new reservoir will be unobtrusive in the landscape and will not come above the height of the embankment of the existing Gray Reservoir. The proposed plans can be viewed at water.ie/stillorgan.