It still tests the water that comes out of the treatment plant and flows to taps, but not the "raw water" in the ground that feeds it.
In early 2024, testing at source ended for the "raw water" – the untreated source water – that's sent to the Bog of the Ring Water Treatment Plant, just southwest of Balbriggan.
However, drinking water is still tested after it comes out of the treatment plant, and before it travels onwards to the 32,000 people who live in what is known as "Fingal Zone 3".
And the water quality has been good the last few years, says Irish Water's online database.
So does the end of the raw-water testing at source matter?
It certainly raises some questions for Irish Water, says Puneeta Sreenivas, freshwater policy officer at the Sustainable Water Network (SWAN).
The main one, she says, is: "Is there scientific proof or rationale behind you not doing this?"
Current regulations require adequate monitoring of raw water, she said, but don't dictate how frequent that is or what is checked for. Those parameters can vary, but just need to be risk-based, she said.
In this case though, it isn't immediately clear that was the case. "That's a concerning situation because the reason seems to be a change in contract," she said. "That's not scientific."
Emails released by Irish Water in response to a request under Access to Information on the Environment Regulations suggest that the change came after outsourcing.
"All regulatory and operational sampling in Fingal areas was previously done by staff of Fingal Co. Council and the samples brought to us for analysis," said the senior executive scientific officer at Dublin City Council's Central Laboratory, to a colleague at Irish Water, in an email last year.
"Weekly sampling at Bog of the Ring was part of the operational work," they said. But in March 2024, the job of drinking-water sampling passed from Fingal to Uisce Éireann, which outsourced the work, they said.
Operational sampling at Bog of the Ring stopped after that, they said.
A spokesperson for Irish Water hasn't yet replied to a query sent on Thursday morning, asking if they had carried out a risk assessment before stopping the monitoring of the raw water.
Sreenivas says monitoring raw water at source acts like an early warning system for drinking water safety.
You can see trouble coming and you can up your treatment requirements within the plant accordingly, she said. "It is in the interests of public health to do that."
Compliance with the European Union (Drinking Water) Regulations is high in Ireland, meaning that its public drinking water is safe to drink, says the Environmental Protection Agency's most recent annual report.
The report does highlight the importance of resilience of the water treatment systems, though.
Testing raw water would be part of that resilience, said Sreenivas. "To make sure the water is managed and monitored appropriately, in preparation for a future where there are alot more unknowns."
###What's the benefit?
Internal emails show a couple of requests from Irish Water analysts for up-to-date data for "raw water" at Bog of the Ring.
In one of the requests, an analyst says that the data will help inform the "crypto monitoring rationale and how if any protozoal deficit will be addressed". Also, "the results of the raw water E.coli monitoring will inform the requirement for any additional treatment," it says.
He got the historic data, up to March 2024 to inform that, the records show.
"Internal requests for monitoring data are common," said an Irish Water spokesperson. "These specific requests were required to support risk assessment and safety planning for the water supply."
Irish Water uses raw water data for several purposes, they said. "This can include risk assessment and safety planning; review of our maintenance programmes; research; and the scoping and/or design of new infrastructure."
But also, they said, "The requirement for raw water monitoring is risk-based. Raw water monitoring is not currently required at Bog of the Ring."
"Uisce Éireann regularly review our monitoring programmes and we may decide to include raw water monitoring at Bog of the Ring in future monitoring programmes, even if there is no regulatory requirement," said the spokesperson.
###The future
There probably isn't any big problem with the raw water feeding into the Bog of the Ring plant, said Sarah Zimmerman, a local Balbriggan resident and environmentalist.
But still, she says, it seems that there would be benefits downstream to testing it.
If contaminants in the drinking water are only picked up later down the line, it causes more hassle for the wastewater treatment plant, she said. "It would require less treatment later on."
Also, it doesn't necessarily follow that because past monitoring hasn't thrown up any problems, it's okay to stop, she said.
A spokesperson for the EPA said that the Drinking Water Regulations 2023 are mostly concerned with monitoring the quality of drinking water that comes out of the tap. That's the "point of compliance," they said.
The regulations also say that an operational monitoring programme should be in place. The scope of that is supply-specific, they said, but must include what is called "turbidity", which is kind of cloudiness, at the water treatment plant.
The Bog of the Ring plant has monitors for that, they said. "At the time of the latest EPA audit in October 2024 online turbidity monitors were in place on the raw water and the treated water."
There are also "continuous online monitors" for the input raw water as it enters the treatment plant, checking pH and dissolved oxygen, they said.
Other considerations are in play too when it comes to appropriate monitoring, they said. "Groundwater sources such as the Bog of the Ring boreholes are less susceptible to rapid changes in raw water quality compared to a surface water source," they said.
"Therefore it is reasonable to expect that the frequency of raw water monitoring at the source boreholes could be reduced, particularly if there is a long history of previous monitoring and if raw water monitoring is in place at the water treatment plant," they said.
A spokesperson for Irish Water said that its approach to raw water monitoring at Bog of the Ring is to be reviewed again in the coming months, as it draws up its 2027 operational monitoring plan.
Sreenivas, of SWAN, says that, under the recast EU Drinking Water Directive, Irish Water has until July 2027 to carry out a risk assessment and risk management plan for catchment areas that feed drinking-water abstraction points.
In other words, a formal analysis of the risks to raw-water quality in the area upstream of where it is taken.
That doesn't mean that Irish Water has to, by law, be testing everything at this point in time, she said. "But the issue here is that they were testing and stopped it," she said.
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