Irish Water plans new €80m reservoir for south Dublin

Utility wants to build a covered storage facility at Stillorgan to end contamination risk

 One of the reservoirs at the Stillorgan facility in Co Dublin. Irish Water is to spend €80m  building a covered water storage facility in Stillorgan. Photograph: Naoise Culhane

One of the reservoirs at the Stillorgan facility in Co Dublin. Irish Water is to spend €80m building a covered water storage facility in Stillorgan. Photograph: Naoise Culhane


Irish Water is to spend €80 million building a covered water storage facility at the 150-year-old Stillorgan reservoir, which provides drinking water for 200,000 people across south Dublin.

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.

“There’s birds flying over it all the time, with the obvious consequences there, and if a cat or dog dies, it could well end up in there.

“And in the summer there are times when people break in to have a swim, so there is a risk of contamination,” said Geoff O’Sullivan, head of major projects at Irish Water.

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 Mr O’Sullivan said this is no longer considered an acceptable solution.

“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.

“Developing a covered reservoir will make the water supply safer and more secure.”


Irish Water plans to apply to Dún Laoghaire-Rathdown County Council for the 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 reservoirs, known as the Gray Reservoir, for the project.

It will then construct the new covered facility within approximately 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 new reservoir will still provide sufficient water for the existing population and to cover population growth over the next 10 to 15 years, Irish Water said.

Irish Water 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 utility is beginning a six-week public consultation programme on its plans from Wednesday.

The proposed plans can be viewed at and submissions on the project can be made until September 14th at or by post to: FAO Stillorgan Reservoir Project, Colvill House, 24-26 Talbot Street, Dublin 1.

Information evenings will be held on August 25th and September 5th at Glenalbyn Sports Club, Glenalbyn Road, Stillorgan, between 4pm and 8pm.