The reservoirs at Stillorgan store treated drinking water from water treatment plants at Vartry in County Wicklow and Ballymore Eustace in County Kildare. These reservoirs are open to the environment which is not in accordance with current best practice as it presents quality risks to the water supply. These risks are being managed, however, they will need to be eliminated through the covering of the stored drinking water. This will ensure a sustainable and secure supply of drinking water for the region.

Irish Water has awarded the contract for the design, construction and commissioning of a new covered storage reservoir at Stillorgan to J. Murphy & Sons Limited.  Construction commenced in November 2018 and is expected to take two years to complete.  

Irish Water’s absolute priority is to protect human health by ensuring the safety and security of the drinking water supply for the 200,000 people served from Stillorgan, while being able to plan for future for growth and development. 


The Stillorgan Reservoir Site consists of three open reservoirs of treated drinking water named the Gray, Upper and Lower Reservoirs.  The main element of work at Stillorgan is to drain the Gray Reservoir and to construct a new covered reservoir within the existing reservoir.  The Upper and Lower Reservoirs will be retained as active reservoirs through the construction period (approximately two years).  Once the new covered reservoir is operational, the Upper and Lower Reservoirs will be drained, decommissioned and their areas reserved for future use.  The base of the reservoirs will be landscaped for visual amenity.

Best international practice insists that treated drinking water supplies should not be stored in open reservoirs where they are susceptible to contamination.  This has to be done to ensure the safety and quality of the water supply. 

Following consultation with stakeholders, Irish Water prepared an Environmental Impact Statement (EIS) which was submitted in support of the planning application. This document set out the impacts (both positive and negative) which the proposed development would have on the environment.

Following preparation of outline designs for the upgrade works, a screening assessment of the potential for environmental effects was completed. This included assessment of whether the construction or operation of the elements are likely to have significant effects on any surrounding environmentally sensitive sites or species protected under European Directives (Habitats or Birds Directives), known as Appropriate Assessment.  The screening assessment concluded that the project would not result in significant adverse effects on protected sites and species. 


It is expected that construction will commence in 2018 and will be completed in a single phase of approximately 24 months. A further 12 months will be required to decommission the active open reservoirs and to landscape the remainder of the site

Works for the Stillorgan reservoir are confined to the existing Stillorgan site.  The most noticeable impact during the works is likely to be on traffic.  Irish Water, and its Contractor, have agreed a traffic management plan with Dún Laoghaire County Council in consultation with the local Garda station.  

Construction traffic will enter the site along St Raphaela’s Road from the north and leave the site along St Raphaela’s Road to the south.  There will be a left turn only entrance to minimise interaction with existing traffic on the road.  A wheel wash will be installed on the site to minimise construction dirt on the public road and road sweepers will be on standby and used when required. Parking of construction vehicles will be on the site. 


Some noise and vibration will result from the construction works. The project requires excavation of some rock to level the site for the construction of the buildings. The Contractor is required to meet the noise and vibration limits set out in the Environmental Impact Statement at the boundary of the Stillorgan Reservoir site.  

Noise and vibration monitors will be installed by a specialist contractor at nominated locations throughout the site.  The vibration data will be recorded and alerts will be distributed to the site project team should the vibration data approach the prescribed limits for the site.
Individual work activities will be re-evaluated should the levels approach the limits set for the site. Records will be compiled and issued to Irish Water during the course of the works.

A specialist contractor has been contracted for proactive pest management throughout the works.  Pest management control is in compliance with best practice from the Campaign for Responsible Rodenticide Use (CRRU).

A security fence with dust and noise reduction netting will be installed along the embankment and maintained for the duration of the construction works.  Monitored site security will be in place throughout the Contract.

The site perimeter will be strengthened where required.  Once the works are complete, the site will remain an active treated water storage area and consequently public access will not be permitted.

Security of the Stillorgan Reservoir site and the water supply from the reservoirs is our priority throughout the project. 

The works are not expected to result in adverse impacts to air quality.  A dust management plan has been prepared to ensure that the creation of dust from site activities is limited.  Dust monitors will be put in place by a specialist contractor at agreed locations around the perimeter of the site to confirm that the dust levels do not exceed the industry standards of 350mg/m2/day. This will be monitored and recorded. 

Individual work activities will be re-evaluated should the levels come near to the limits set for the site. Records will be compiled and issued to Irish Water during the course of the works.

The upgrade at Stillorgan Reservoir is being designed and assessed at the same time as works to upgrade the Vartry Water Treatment Plant, Reservoir and Pipeline.  However, the upgrade works to the Stillorgan Reservoirs are required irrespective of the proposed work at Vartry to meet best practice for the storage of treated drinking water prior to supply. Over half of the water at Stillorgan is now sourced from the Ballymore Eustace Water Treatment plant.

The new covered reservoir will have the capacity to support future growth to 2031. The remainder of the site needs to be reserved for future water services infrastructure to secure drinking water for the community. The site will remain a live drinking water storage, treatment, and distribution centre for over 200,000 customers.  

The Stillorgan reservoir site will remain a strategically important part of Dublin’s water services infrastructure for the long term.


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