Stillorgan Covered Reservoir: improving water safety in Dublin


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Situated in south Dublin, the new covered reservoir is ensuring a safer, more sustainable water supply for more than 200,000 residents.

Originally constructed as part of the Vartry Water Supply Scheme, the Stillorgan open reservoir served south Dublin for over 150 years.  

At the time, this scheme significantly improved sanitation in Dublin. However, as one of the last remaining reservoirs of its kind in Europe where treated drinking water is left exposed, there was a risk to water quality.   

A major upgrade of the facility was therefore urgently needed. As part of a design and build contract with the Irish engineering and construction company Murphy Ireland, we were appointed to deliver design services for this ambitious project for Uisce Éireann (Irish Water).  

Completed in 2022, the upgrade has not only modernised the aging infrastructure, but is also ensuring a clean and secure water supply for the local community.  

The new Stillorgan Covered Reservoir will provide capacity to support future water demand up to 2031. 

What was AECOM’s role on the Stillorgan Covered Reservoir?  

With capacity to store 160 million litres of covered storage for treated drinking water (the equivalent of over 60 Olympic-sized swimming pools), as well as a plant for secondary disinfection, the new reservoir was a major undertaking requiring effective collaboration and planning.  

Initially, the 16-hectare site comprised three separate reservoirs: Gray, Lower and Upper. The challenge was to implement a phased modernisation plan, replacing them all with a new covered service reservoir, whilst limiting disruption to existing water supply services.  

Our work encompassed the full civil and structural, hydraulic and geotechnical design services for the new service reservoir and access roads.  

In addition, we acted as Project Supervisor Design Process (PSDP) – the equivalent of the UK Principal Designer role – and provided both environmental and landscape architectural services. 

Following the draining of the Gray reservoir, we worked closely with the client throughout the two key phases of the project. First, to ensure the continuity of portable water supply from the two existing open reservoirs (Lower and Upper) while the new covered service reservoir was under construction.  

Secondly, to decommission the remaining open reservoirs and connect the final pipework to complete the transition. 

Upgrading infrastructure and services 

In addition to the core elements, we were required to design a new site entrance, an internal access roadway and bridge over the Carysfort-Maretimo stream, pipeline modifications and improvements.   

Our team was also responsible for designing connections to existing inlet and outlet pipelines, sustainable drainage systems (SuDS) and stormwater attenuation, green roofing and comprehensive landscaping.   

As the first design and build project of this scale delivered under building information modelling (BIM) Level 2, this project required the use of a common data environment to manage the design and contract. By using the clash detection reports generated from 3D design modelling, we were then able to identify any potential issues to be resolved in the design. 

We also used 3D Revit models for some of the complex pipe connection works in the outlet chamber. This ensured that when fabricated pipe fittings and bends arrived on site, they didn’t require any cutting or modifications and could be installed as designed – helping to streamline the delivery process. 

Meeting the water demands of current and future generations   

By replacing the open reservoir site with a covered service reservoir, this project has directly reduced contamination risks from wildlife, airborne materials and human interference – delivering substantial health benefits for the local population.  

As well as ensuring a safer and more secure water supply for communities across south Dublin, the new Stillorgan Covered Reservoir will also provide capacity to support future water demand up to 2031.