Cambridge Water under fire after toxic PFOS chemicals found in tap water.

Cambridge Water has been heavily criticised by inspectors for a “catalogue of errors” which left customers potentially exposed to toxic chemicals in their tap water during a five-month spell.

The Drinking Water Inspectorate (DWI) condemned the company for failing to meet “the minimum expectation of a water supplier” and for damaging the reputation of the whole industry by causing the public to lose confidence in the water supply.

Cambridge Water failed to have “a system of control” that would have prevented unacceptable levels of toxic chemicals reaching customers’ taps, according to the DWI’s damning report.

More than 1,200 customers in Sawston, Hinxton and Stapleford are believed to have been affected. Sampling showed they were exposed on at least three occasions to PFOS (perfluorooctanesulfonic acid) chemicals at three times the level set by the government as an acceptable limit.

PFOS chemicals are linked with increased cholesterol, low birthweight and suppressed immune response. They are known as “forever chemicals” because of their persistence in the environment.

The report found Cambridge Water delayed testing water samples or acting on the results of tests, which meant the Duxford aquifer, the root of the contaminated water, was not taken out of service until June 2021.

The DWI report said: “Errors, inaction and incorrect assumptions resulted in five months of unnecessary delay in removing the site from supply. The company did not meet the minimum expectation of a water supplier, and this has resulted in the public losing confidence in the water supply and is reputationally damaging for the water industry.”

It added: “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.

“Had the company made valid and more robust assumptions with regards to the likely true flow rates from sources, it would have appreciated the risk of supplying water containing PFOS levels exceeding 0.1 μg/l. These assumptions, errors, mistakes and misinformation are not commensurate with the diligence required of a water company to supply drinking water and this goes towards the loss of confidence by the public. This position is unacceptable.”

The report details how in spite of contamination of the water supply to parts of South Cambridgeshire being “obvious”, there were months of unnecessary delays before the affected aquifer was removed from Cambridge Water’s supply system.

The company had tried unsuccessfully to blend the Duxford aquifer water with an untainted supply to bring the toxic chemical level within government guidelines. However, the report states that Cambridge Water finally had to admit it was unable to guarantee that the water contamination would consistently fall below government limits due to limits on the amount of water it was able to extract from the clean source.

Cambridge Water has estimated 1,279 properties may have received unblended supplies on these occasions 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 government limit is less than 1µg/l. There were 1,113 properties affected in Sawston, 154 properties in Hinxton and four properties in Stapleford.

PFOS, or perfluorooctanesulfonic acid, is a member of the PFAS group of chemicals, which stands for per- and poly-fluoroalkyl substances. These are a common component of some firefighting materials which were known to be used at Duxford Airfield in the past. They are believed to have leached through the ground into the water table.

For decades, PFAS products have been used in hundreds of industrial applications and consumer goods such as carpeting, apparel, upholstery, certain food paper wrappings, metal plating, and firefighting foams. Firefighting foams were a significant source of PFAS risk in and around airports that could end up seeping into the ground and contaminating ground water.

Duxford Airfield pumping station is located within the former air force base that is now the Imperial War Museum site near Duxford. There are two borehole abstractions on site. The water is then pumped to Cambridge Water’s nearby works, Sawston Mill, for treatment and onward distribution to consumers in the Cambridge rural water supply zone. However, pumping has ceased at the site until Cambridge Water is able to ensure its processes will result in safe tap water.

The report states that Cambridge Water only notified the inspectorate about the contamination issue on February 8, 2022 – the day The Guardian newspaper published a story about the problem, even though samples showing the contamination had been taken the previous year.

It also notes that Cambridge Water took no action to inform customers of the presence of PFOS in its water supplies before it finally closed down the Sawston Mill site which produced the water from the Duxford aquifer.

And the water company gave “incorrect information” on its website after news of the contamination was published in the national press. It claimed “levels of PFAS at customer taps were at, or around, the Tier 1 (lowest risk) level”.

However, the report states this was not correct because the company had identified PFOS concentrations above 0.1µg/l at three consumer taps between April and June 2021, therefore making them Tier 3. In addition to this, on February 12, 2022, the company sent a letter to all consumers within the affected areas which referred to a “small number of Tier 2 samples” from Duxford Airfield. These samples should have been referenced as Tier 3.

The report notes that Cambridge Water eventually changed this statement on their website in November last year.

A toxicologist concluded: “It is not possible to definitively state whether exposure would be sufficient to cause potential health effects but that also applies to the 0.1 µg/l value in view of the uncertainties involved.”

As a result of this uncertainty, the inspectorate could not recommend prosecution of Cambridge Water under the amended Water Supply (Water Quality) Regulations 2016. Instead, he made a series of recommendations, including that it updates its risk assessment processes.

Cambridge Water released the following statement in response to the report: “The Drinking Water Inspectorate has today released a report regarding a water event in the South Cambridge area, which is supplied by Cambridge Water.

“This report relates to a historic issue regarding levels of PFOS in the water supply that is connected to the Duxford Aquifer. Since 25th June 2021, the Duxford Aquifer has been isolated from our system so it is not supplying any water.

“This is to allow for us to finalise the improvement works we are making to the water treatment process ensuring the highest levels of safety before the water from Duxford Aquifer is reintroduced into the supply. The water supplied to the South Cambridge region is safe to drink.

“We have co-operated with the DWI’s review and thank them for their detailed report into this matter. We apologise to our customers for the errors that were made at the time and note the recommendations made by the Inspectorate.

“We have already taken steps to improve our processes and will take forward the additional measures the DWI has outlined. We are committed to providing high-quality water to all of our customers.”