The latest annual report from the Drinking Water Quality Regulator for Scotland shows that Scottish Water’s compliance with the standards for drinking water in 2013 has continued to improve.

The DWQR monitors the quality of water samples taken by Scottish Water, enforces serious breaches of the regulations and checks Scottish Water are taking and analysing samples correctly. The regulator also inspects Scottish Water’s assets and activities and oversees the water company’s quality-driven investment programme.

Scottish Water take and analyse samples of drinking water from across Scotland 365 days a year. In 2013 a total of 330,156 regulatory tests were carried out on Scotland’s drinking water. Of those taken from consumers’ taps, 99.89 per cent met the required standards. This continues the improving trend since Scottish Water was formed in 2002 when 99.28 per cent of samples met the required standards.

The 252 water treatment works (WTW) around Scotland, which vary considerably in size, are also sampled regularly. In 2013, 72,209 tests were carried out on samples collected at treatment works. The main compliance parameters are microbiological – coliforms and E. coli. In 2013, only 17 samples contained coliforms and 1 contained E. coli. This represents a significant improvement on past years with detections of both parameters around half those in 2012, and represents the best ever microbiological compliance.

The report states:

“Water treatment works performed well in 2013, reflecting delivery of investment, improved sampling arrangements and significant efforts by operational staff. DWQR inspections of works have generally shown treatment works to be adequately equipped and well managed. Among site specific issues identified, some common themes emerged, including a need to more comprehensively assess and respond to important risks to water quality, including the need for additional water quality monitoring where a risk has been identified.”

“Work to fully understand the operation of key parts of the treatment process and the science behind these at some sites is beginning to bear fruit. It is vital Scottish Water continues this work and challenges long-standing assumptions and operational practices where appropriate. Nowhere is this more apparent than with Cryptosporidium and the need to investigate detections and assess plant performance against well-documented industry best practice to ensure the necessary resilience is built into all treatment processes.”

Three significant disinfection failures in 2013

Scottish Water is required to tell DWQR about all events that could adversely affect water quality or cause concern to consumers. In 2013, 419 such events were notified to DWQR, a significant reduction on previous years.

DWQR considers each event and classifies them - the more serious ones are declared incidents and In 2013, 24 events were classified as incidents, described as “a sharp drop on 2012.2 However, the regulator said that once again, the number of incidents that were caused by a failure of the disinfection process is too high and flagged up  three significant incidents occurred in 2013:

• Tomnavoulin WTW, Moray
Cryptosporidium was detected in the supply, which has had a history of problems of this nature. DWQR said “it is evident that the measures put in place previously to address problems  in 2012 at the works have not been completely effective.”  Scottish Water has replaced membranes, installed additional monitoring and is continuing to investigate the situation. DWQR has visited the site and has been engaged in ongoing dialogue with Scottish Water concerning the resilience offered by the plant.

• Bradan WTW, Ayrshire 
Bradan water treatment works suffered a failure of the disinfection process for nearly three hours. Further investigation established that an isolation valve from the standby chlorine drum was in a closed position and the drum appeared empty when it was in fact full. Emergency chlorine dosing to the clear water tank was used until the issue was rectified and prevented any impact on the quality of water supplied to consumers.

• Storr Forest WTW, Skye
• Cryptosporidium was detected in large quantities in a sample taken from this basic supply. Further detections continued at lower concentrations through the Autumn until clear samples were eventually obtained in November. Storr Forest is vulnerable to changes in raw water quality as there is no filtration process and there has been a history of intermittent Cryptosporidium previously in the supply.

Private supplies remain a concern

Around three per cent of the population in Scotland - 150,000 people - receive their water from  private water supplies, many of which have limited or no treatment. The main risk comes from microorganisms, including E.coli. Strengthened regulations governing the quality of private water supplies were introduced in 2006.

However, the regulator said the quality of some of the supplies remains of concern - 13.6 per cent of samples taken from type A supplies last year contained the E.coli bacterium.

Sue Petch the Drinking Water Quality Regulator said:

“Scottish consumers can be confident that their drinking water is thoroughly tested and that it meets some of the highest quality standards in the world.

“It is satisfying to be able to report a high level of performance, which reflects Scottish Water’s efforts over the past year. This by no means indicates that further improvements cannot be delivered. Work is still needed to make sure that all of Scotland’s water assets are well maintained and sufficiently resilient to deal with challenges presented by changing source water quality.

“It is important that the quality of private water supplies improves, and there remains much to do here. DWQR is working with local authorities and other stakeholders to make owners and users aware of the health risks their private water supplies could present. “

Click here to download Drinking Water Quality in Scotland 2013.