Minutes published in July reveal that Scottish Water, SEPA and the Scottish Government do not share the same understanding of the baseline for a national sewer-overflow improvement programme. The economic regulator is also asking why projects have moved into later investment periods — and what customers received from investment made instead.
Scotland has a programme to improve some of its most problematic sewer overflows. Five years after that work began, the organisations responsible for delivering, regulating and overseeing it are still trying to establish precisely what the starting commitment was.
Minutes of the Water Industry Investment Group, published by the Scottish Government on 16 July 2026 following a meeting on 11 March, record an unusually direct disagreement involving Scottish Water, the Scottish Environment Protection Agency, the Scottish Government and the Water Industry Commission for Scotland. The discussion concerned the Improving Urban Waters Routemap and the programme of work associated with sewer overflows classed as unsatisfactory.
Combined sewer overflows are built into wastewater networks as safety valves. During heavy rainfall, when the volume entering a combined sewer exceeds its capacity, an overflow can release diluted wastewater into a river, burn, loch or coastal water rather than allowing sewage to back up into homes, businesses and streets. Their existence does not in itself indicate a failing sewer. Problems arise where an overflow operates in dry weather, contributes to poor water quality, releases excessive sewage-related debris or fails to meet licence conditions.
Scottish Water says it has more than 4,080 overflows across its network. Around 3,200 have been assessed as satisfactory and around 900 as unsatisfactory. From those, studies identified 108 high-priority assets for improvement.
It is the status of those 108 that produced the disagreement recorded in March.
The Scottish Government challenged the baseline Scottish Water was presenting, saying it did not align with the original commitments or with SEPA’s expectations. Scottish Water said there had been an original list of 108 sites but argued that “a formal baseline had never been established”, adding that delivery numbers had always depended on the funding available and that there would be competing demands for investment in the next regulatory period.
SEPA’s position was different. It told the group that 108 represented its baseline expectation, said it had written to Scottish Water and indicated that it was moving towards a regulatory position. Scottish Water and SEPA had already been discussing detailed site lists and arrangements allowing projects to be substituted where necessary.
The disagreement becomes more concrete when the programme is narrowed to overflows known to affect water quality.
SEPA identifies 24 combined sewer overflows in the 2021–27 River Basin Management Plan as affecting water-quality classification. At the March meeting, the Scottish Government said only 19 of those 24 were expected to be delivered. Scottish Water agreed to check the number of relevant River Basin Management Plan projects, so 19 should not yet be treated as a final reconciled total.
The Water Industry Commission for Scotland then raised a separate concern: when the remaining work would actually be done.
WICS expressed concern that a “significant number” of projects to address unsatisfactory intermittent discharges were being rephased into the next investment period, SR27, which runs from 2027 to 2033. According to the minutes, the regulator asked why delivery had slipped, why projects were being moved and what Scottish Water had invested in during the current period instead. The meeting recorded that there was “not yet full confidence in the proposed baseline.”
Scottish Water acknowledged that the timetable extends further still. It told the group that some projects had moved into the Strategic Review 2033–39 period, known as SR33. SEPA separately confirmed its view that some investment intended for the current SR21 period had been rephased into SR27.
Those statements do not mean that all 108 high-priority overflows were originally due to be fixed by 2027.
Scottish Water’s published framework assigns different indicative timescales according to the problem being addressed. For high-priority overflows affecting water quality, the indicative delivery date is 2027. For high-priority overflows that spill during dry weather or cause serious sewage-related debris, it is 2031. Scottish Water states explicitly that those timescales are subject to investment prioritisation and planning.
The numerical picture has also changed as engineers have studied the network.
Scottish Water says that, since the routemap was published in December 2021, it has been developing solutions for the original 108 high-priority UID needs while also examining medium-priority sites and other overflows connected hydraulically to them. It now has 145 UIDs in development and predicts 97 solutions will be completed before December 2027. Some high-priority sites in densely connected urban sewer systems have proved to require much more extensive investigation and engineering than initially understood.
That means 108 sites, 145 UIDs and 97 solutions cannot legitimately be treated as three comparable totals. One engineering solution may involve several connected assets; priorities can change as more is learned about a sewer catchment; and some proposed interventions can be substituted or redesigned.
The problem identified in the March meeting is therefore not an unexplained arithmetic gap between 108 and 97. It is the absence of a common baseline against which changes to the programme can be followed from one investment period to another.
That problem had already attracted scrutiny from outside the water industry.
Environmental Standards Scotland concluded in September 2024 that there was no comprehensive, publicly available picture of the scale and environmental impact of storm-overflow spills in Scotland. It recommended that Scottish Water publish an accessible improvement plan identifying the locations requiring work, the timetable for each and, where no timetable had been settled, when a decision would be made.
The watchdog did not conclude that Scotland’s wastewater system was simply deteriorating. Its investigation found substantial long-term improvement: wastewater was identified as a pressure on 208 surface water bodies in the Scotland River Basin District in 2008, falling to 48 in 2020. It also cautioned that the condition assigned to a whole river or other water body can mask more localised effects from sewage discharges.
SEPA likewise records a long history of investment. Between 2010 and 2021 it required Scottish Water to improve 279 sewer overflows and 104 wastewater treatment works because they were causing significant pollution. It currently says 87 per cent of Scotland’s waters have good or better water quality.
Scottish Water’s present Improving Urban Waters programme is backed by around £500 million of investment and includes sewer upgrades, treatment works, monitoring and measures intended to reduce the effects of overflow events. Its original routemap was published in December 2021 and has been followed by annual updates. The company has also substantially expanded overflow monitoring and publication of data since the programme began.
The timing dispute is arising just as Scotland decides how much Scottish Water should be allowed to raise from customers during the next investment period.
On 30 June, WICS published its draft determination for 2027–33. The regulator describes the process as setting the maximum amount Scottish Water can charge customers while determining the investment programme and service improvements those charges are expected to fund. The consultation remains open until 1 September.
Household water and wastewater charges increased by 8.67 per cent in nominal terms for 2026–27. WICS says that adds about £42 a year to the average household bill. The increase funds Scottish Water’s wider service and investment requirements and cannot be attributed specifically to sewer-overflow projects, but it explains why the regulator’s question about rephased investment goes beyond an internal disagreement over spreadsheets.
The same March minutes show Scottish Water forecasting total investment of £1.126 billion in 2026–27 against a planned £1.210 billion, a difference of £84 million. Scottish Water explained that the gap represented headroom needed to retain flexibility for responsive investment. There is therefore no basis in the minutes for describing £84 million as a simple cut or underspend.
What the records do show is that work expected within one regulatory framework is now, in some cases, appearing in the next one or even the 2033–39 period, while Scottish Water and its environmental regulator maintain different positions about the original baseline.
By April 2027, the Improving Urban Waters Routemap will have been running for more than five years. A single public record showing the original high-priority sites, what has been completed, what has been redesigned or substituted, what remains outstanding, and which work has moved into later investment periods would allow genuine changes in engineering need to be distinguished from deferred commitments.
Without that common ledger, projects can move from one six-year investment period to another while every organisation involved remains capable of describing its own figures accurately.
Sources
Water Industry Investment Group Minutes: March 2026 — Scottish Government — Published 16 July 2026
https://www.gov.scot/publications/water-industry-investment-group-minutes-march-2026/
Improving Urban Waters Routemap — Scottish Water — Original Routemap Published December 2021
https://www.scottishwater.co.uk/Help-and-Resources/Document-Hub/Key-Publications/Urban-Waters-Improvements
Improving Urban Waters Routemap — Scottish Water
https://www.scottishwater.co.uk/about-us/what-we-do/urban-waters-routemap
Prioritisation Of Sewer Overflows In Scotland — Scottish Water
https://www.scottishwater.co.uk/Your-Home/Your-Waste-Water/Overflows/Prioritisation-of-Sewer-Overflows-in-Scotland
Published Overflow Data — Scottish Water
https://www.scottishwater.co.uk/Your-Home/Your-Waste-Water/Overflows/Overflow-Event-Data
Improving Urban Waters — Scottish Environment Protection Agency
https://www.sepa.org.uk/environment/water/improving-urban-waters/
Storm Overflows: An Assessment Of Spills, Their Impact On The Water Environment And The Effectiveness Of Legislation And Policy — Environmental Standards Scotland — 4 September 2024
https://environmentalstandards.scot/our-work/our-analytical-work/storm-overflows-an-assessment-of-spills-their-impact-on-the-water-environment-and-the-effectiveness-of-legislation-and-policy
2027–33 Draft Determination — Water Industry Commission For Scotland — 30 June 2026
https://www.wics.scot/publications/price-setting/strategic-review-charges-2027-33/determinations/2027-33-draft-determination
2027–33 Draft Determination Consultation — Water Industry Commission For Scotland — 30 June 2026
https://wics.scot/consultations/price-setting-consultations/2027-33-draft-determination-consultation
Charges Scheme For 2026–27 — Water Industry Commission For Scotland — 23 January 2026
https://wics.scot/publications/price-setting/strategic-review-charges-2021-27/scottish-waters-charges-scheme/charges-scheme-2026-27
Scottish Water Announces 2026–27 Charges — Water Industry Commission For Scotland
https://wics.scot/latest/scottish-water-announces-2026-27-charges
