The Drinking Water Quality Regulator for Scotland has flagged up the “deteriorating condition and age” of many of Scottish Water’s assets and concerns that the current scale and pace of investment in the maintenance and replacement of water assets is "simply not sufficient."

Writing in the Foreword to  the newly-published Drinking Water Quality in Scotland 2023 DWQR Annual Report – Public Supplies, Matt Bower Drinking Water Quality Regulator for Scotland said he was proud to report that the quality of Scotland’s drinking remains amongst the finest in the world.

However, he went on to warn:

“As we travel around Scotland, visiting and inspecting Scottish Water’s treatment works and storage points, my team and I are often struck by the deteriorating condition and age of many of these assets. In some cases, good performance is only achieved by the ongoing effort and diligence of Scottish Water’s operational staff. In times of challenging source water quality, treatment processes that are nearing the end of (or beyond) their planned lifespan may lack the processes and control systems needed to consistently meet quality requirements.

“As the effect of climate change introduces additional variability, I am concerned that the current scale and pace of investment in the maintenance and replacement of water assets is simply not sufficient to safeguard the consistently high quality of our drinking water for future generations.”

Scottish Water takes and analyses its own samples to demonstrate that the water supplied complies with regulatory requirements. Samples are taken from drinking water as it leaves water treatment works (WTWs), service reservoirs (SR) (also referred to as storage points) and from randomly selected consumers’ taps.

Water that has been treated to a high standard can deteriorate if the storage tanks designed to hold it on its way to consumers are not maintained, allowing the ingress of contamination. In 2023, following several serious incidents, DWQR issued a Scotland-wide enforcement notice to Scottish Water, requiring the company to improve its performance in this respect so that all storage points will be inspected and maintained on a regular basis.

Water quality standards change over time - 2023 saw the introduction of a number of new parameters as a result of Scotland’s alignment with the recast European Drinking Water Directive – the only UK nation to do so to date.

Scottish Water complied with most of the new standards from the outset, with the exception of two – chlorate and haloacetic acids. Both of these relate to the use of chlorine as a disinfectant, an essential part of the treatment process. Chlorate may be controlled through good housekeeping of chemical stocks, and although 2023 saw twenty-three failures of this standard, the situation has improved considerably so far in 2024.

DWQR says this will however need to be the subject of ongoing efforts by Scottish Water, which will be monitored as part of the DWQR audit programme.

There were ten failures of the haloacetic acid standard, and although some optimisation of treatment processes will assist in controlling their formation, there are at least three sites where investment is likely to be required. Matt Bower says DWQR has sought a commitment from Scottish Water to ensure that this happens in a timely manner.

In 2023, Scottish Water carried out a total of 272,017 regulatory tests on Scotland’s drinking water and many more for operational reasons such as following a burst main.

Of the 113,454 tests taken in 2023 to represent water at consumers’ taps, 99.88% complied with the standards. A further 62,253 tests were carried out on water supplied from treatment works and all but 30 of these tests met the required standards - a slight deterioration on the previous year’s performance. 96,310 tests were also taken from service reservoirs (SR), where treated water is stored. Compliance here was also poorer than in the last few years, due to an increase in detections of coliform bacteria.

The rise in coliform detections is one of the factors leading to DWQR serving an enforcement notice for inspection and maintenance of storage points on Scottish Water.

Scottish Water is required to tell DWQR about any event that could affect water quality or cause consumer concerns. There were 921 water quality events reported in 2023. Events of a more serious nature are categorised as water quality incidents. In 2023, 29 events were declared to be incidents and investigated by DWQR. As in previous years, significant loss of control of the water treatment process and issues causing significant customer concern were the most common cause of incidents. During 2023, 21 incident and event investigation visits or audits took place. 14 at water treatment works and seven distribution activities.

Scottish Water CEO welcomes DWQR support for need to increase investment in ageing assets and to adapt to changing climate

Commenting in response to the DWQR Report, Scottish Water's Chief Executive Alex Plant said:

“We are delighted that the DWQR has reported that the quality of Scotland’s drinking water remains ‘among the finest in the world’ – with 99.88% of more than 272,000 regulatory tests meeting the required standards - and we welcome his support for the need to increase investment in ageing assets and to adapt to a changing climate.

“The biggest impact on total compliance in 2023 was microbiological performance at Treated Water Storage Points (TWSPs). We have more than 1200 of these assets and we have seen an increasing number of challenges in meeting strict water quality standards, mostly due to their age and persistent heavy rainfall resulting in ingress into tanks and a deterioration in water quality.”

“We are making good progress in carrying out improvements to these TWSPs. We recognised this risk as a key area and delivered record investment in the past year and will sustain this to address the risk to water quality.

“Many assets across our network are ageing and will need extra maintenance before ultimately needing to be replaced. Most were not designed to cope with the type of weather conditions which are now the norm due to Climate Change. This makes it ever more difficult to continue to improve drinking water quality. But we outlined in our Climate Change Adaptation Plan an estimate that over the next 25 years we will need an additional £2 billion to £5 billion above existing expected investment to maintain services.”

Click here to download Drinking Water Quality in Scotland 2023 DWQR Annual Report – Public Supplies