Stillorgan Reservoir Disinfection Upgrade





€3.4 million


In 2015, Ryan Hanley was commissioned by Irish Water to design and administer the Stillorgran Reservoir Disinfection Upgrade. The reservoir had been included on the Environmental Protection Agency (EPA)s Remedial Action List (RAL) due to the absence of a Cryptosporidium barrier. The successful implementation of the project, which involved the construction of the largest UV disinfection plant in Ireland, assured the safety of the water supplied to over 200,000 consumers in the Dublin region.


The benefits to Irish Water and their South Dublin consumers have been:

  • The Stillorgan supply was removed from the EPA RAL thereby securing the safety of the water supply to over 200,000 people.
  • The project ensures that drinking water distributed from the Reservoir meets the Regulations by providing a verifiable primary disinfection system and Cryptosporidium barrier.
  • The adaptation of the existing chlorination system at Stillorgan, as a secondary disinfection system, affords Irish Water and Dublin City Council improved control of chlorine residuals within the five downstream network supply zones supplying Dublin City, Dun Laoghaire and parts of South Co Dublin, thereby quality assuring the safety of the water supply to consumer taps.

Project Details

Client: Irish Water

Location: Dublin

Value: €3.4 million

The Stillorgan Reservoir Disinfection Upgrade Contract involved the following scope of works designed and commissioned by Ryan Hanley at or adjacent to the existing outlet Valve House at the site:

  • Installation and commissioning of flow meters and strainers on each of the 700mm supply mains from the existing Screen house
  • A900mm diameter manifold inside the Reservoir outlet Valve House to accommodate three new proposed UV piped streams including UV reactors, bends, tapers, tees, actuated flow control valves, air valves, scour valves, and flow measurement
  • Installation and commissioning of the associated UV Ballast Panels and supervisory SCADA control panels
  • Adaptation of the existing chlorine disinfection system at Stillorgan including the necessary relocation of the existing chlorine dosing points to points downstream of the UV reactors complete with flash mixing as the secondary disinfection system for chemical residual generation to assure the drinking water quality throughout the distribution system to the consumer tap
  • A new 630 kVA ESB substation to supply the UV reactor control panels complete with metering switch room and all associated electrical works including provision of LV ducting to the valve house, a new Main L.V Switchboard, a complete main cableway system, installation to three new control panels, L.V earthing network, emergency lighting and small power installation
  • Replacement and commissioning of existing 700-1200mm diameter electromagnetic flow meters to facilitate accurate flow proportional control of secondary chlorine dosing in combination with feedback control using residual monitoring
  • Diversion of existing site services including surface water drainage, telemetry to valves and flow measurement, site lighting, Eircom and ESB services in the location of the proposed flow control chamber.
  • Upgrade of the existing SCADA system, incorporating digital screen mimics of UV primary disinfection, the reconfigured chlorine disinfection, the electrical upgrade and the upgrade of the existing Valve House flow mimic to include manifold, additional flow measurement and flow controllers and the provision of continuous monitoring UVT and chlorine residual instrumentation to facilitate remove plant operation.
  • Automation of all existing and proposed distribution main flow control valves (downstream of UV manifold) to allow remote flow control via SCADA.


The construction phase of the project was subject to severe spatial constraints within the existing Stillorgan Valve House and involved complex works interfaces with an existing live trunk distribution manifold, which was required to provide uninterrupted supply a large area of Dublin City during the project works.

The construction of the pipe manifold required planned and sequenced construction interfaces to minimise the impact on Irish Water’s consumers. The detailed planning of the manifold interfaces was extremely successful and resulted in no disruption to the continuity of supply to consumers during the project works. This was achieved by incorporating additional valving arrangements into the new manifold design and carrying out the construction interface works at times of minimum flow.