New Stillorgan reservoir to ensure safer water supply for south Dublin

Irish Water says €50m upgrade to 150-year-old reservoir delivered on time and in budget

More than 200,000 Dubliners will benefit from a safer and more secure water supply following completion of the new Stillorgan reservoir by Irish Water.

The original reservoir in south Co Dublin – the largest treated water reservoir in the country – had supplied drinking water to the surrounding area for over 150 years. It was one of the last remaining uncovered treated water reservoirs in Europe.

Treated drinking water was being left exposed to the elements, with consequent risk of contamination. It also meant losses were more pronounced during drought conditions. The project involved draining down and decommissioning three existing reservoirs at the site, and construction of a new covered reservoir within the footprint of the largest reservoir.

John Prendeville, project manager with Irish Water, said it was a €50 million investment in providing a long-term solution "to safeguard this strategically important part of Dublin's water supply for the future".


“The new reservoir has the capacity to store 160 million litres of treated drinking water – that’s the equivalent of over 60 Olympic-sized swimming pools,” he added.

It was delivered on time and to budget, Mr Prendeville said, through "a hugely collaborative effort between Irish Water, Dublin City Council, Nicholas O'Dwyer Ltd, Murphy International Ltd and of course, the local community, whose co-operation and patience have allowed these works to succeed".

The site was originally constructed as part of the Vartry water supply scheme. It includes two reservoirs at Roundwood, Co Wicklow, a water treatment plant, a four-kilometre-long tunnel under Callowhill and 40km of trunk mains to deliver water to the Stillorgan reservoir. Work began on the upgrade in 2018 with the draining down of the Gray reservoir, which had not been fully drained since it was built in the late 1800s.

Key component

The reservoir, located on land between Sandyford industrial estate and St Raphaela’s secondary school, is a key component of Dublin’s strategic water infrastructure, which links supply from five major water treatment plants through an integrated network of trunk mains and reservoirs.

The project is part of a €150 million upgrade of the Vartry scheme which will secure drinking water supply for the area for decades to come. “Once completed, the upgrade will provide a safer, more secure water supply to the people of north Wicklow and south Dublin,” Irish Water said.

The National Development Plan published on Monday confirmed funding to pipe water from the Shannon river to the Dublin region at a cost of more than €1 billion. The project, due to be completed by 2030, is to ease demand from 40 per cent of the Irish population and to end over-reliance on the river Liffey. It will involve abstraction of water at Parteen Basin in Co Tipperary, treatment nearby, and building a 170km pipe to a reservoir at Peamount, Co Dublin.

Kevin O'Sullivan

Kevin O'Sullivan

Kevin O'Sullivan is Environment and Science Editor and former editor of The Irish Times