Cambridge Water knew of breach but quality watchdog finds no case for offence

The Drinking Water Inspectorate has confirmed in a report last week that levels of a hazardous chemical in water supplied by Cambridge Water in 2021 and 2022 had exceeded permitted levels but the watchdog concluded that there was insufficient evidence that an offence had been committed.

The inspectorate found that Cambridge had exceed the 0.1 µg/l limit for PFOS intermittently between January 2021 and February 2022. But it conceded there was insufficient evidence that Cambridge Water had committed and offence under the Water Supply (Water Quality) Regulations 2016 after seeking advice from independent toxicologists.

The toxicologists reported that the water quality data available was “inconclusive that the concentrations would cause a significant probability of harm to consumers, compared to exposure of PFOS concentrations up to the 0.1 μg/l guidance limit.”

They added that their conclusion “also applies to the 0.1 µg/l value in view of the uncertainties involved,” according to the inspectorate’s report.

The uncertainties arose largely from the Cambridge’s arrangement of blending water from its Duxford Airfield/Sawston Mil works with water from its Abington Park/Hinxton Grange plant. The blending practice had been in place from 2021 when the permitted level for PFOS was decreased in 2020 from 1 µg/l to 0.1µg/l following new reports of the toxicity of PFOS and other similar chemicals.

However blending failed to enable the water company to guarantee that the PFOS level was below 0.1 µg/l. And flow rate evidence from Abington Park/Hinxton Grange had indicated that levels were “more likely to nearer 0.146 µg/l in the network,” based on the known levels in the water from Duxford.

And the inspectorate reported three occasions when when Abington Park/Hinxton Grange were out of supply for more than 11.5 hours and it was possible that Duxford water could have been supplied directly to customers… and therefore may have received PFOS levels of around 0.3 µg/l and up to a maximum of 0.394 µg/l for limited periods.”

The inspectorate concluded that “in January 2021 the company had sufficient information to consider that the supply would likely exceed the newly issued guidance.” But it went on to say the company “made a catalogue of errors resulting in delays from the time guidance was issued to the removal of the Duxford borehole from supply. These included invalid assumptions used for the blending treatment process, failure to apply a risk assessment methodology expeditiously, sampling errors, delays and assumptions.”

The inspectorate report followed its notification by Cambridge Water in February last year, of the presence of perfluorooctanesulphonic acid (PFOS) in supplies from the water firm’s Duxford Airfield/Sawston Mill treatment works. The notification came on the same day as the contamination was reported in a national newspaper story.

The Inspectorate found that PFOS in the supply arose from firefighting activity at Duxford airfield where PFOS was used on aircraft as a fire extinguisher. According to the inspectorate, runoff of the foam penetrated the aquifer from which Cambridge Water used for abstraction. “The water company was not responsible for this ground contamination but was aware of its presence in historical data.” the inspectorate reported.