The Water Industry Commission for Scotland (Wics) has raised concerns over delays in Scottish Water’s investment programme in its five year regulatory period report.

The regulator said that delays in implementing improvements to water treatment works and wastewater discharges have resulted in delays to customer and environmental benefits.

Some of these delays have been as a result of Scottish Water assessing the scope for efficiency savings, although Wics adds other issues arose around design and delivery.

However, Scottish Water has acknowledged the delays and has provided assurance that the remaining projects will be delivered as soon as possible and that measures have been put in place to improve asset management mechanisms for 2015-21.

The Wics report does highlight that Scottish Water has invested £2.5 billion since 2010 in maintaining its assets, with £1 billion of that going on improving water quality.

This has helped create the “significant improvement” in both drinking water quality standards – up from 98.43 per cent in 2009/10 up to 99.74 per cent in 2014/15 – and wastewater pollution incidents – down from 804 in 2009/10 to 249 in 2014/15.

Over the 2014/15 regulatory period, Scottish Water also recorded £122 million of outperformance, which resulted in household bills being kept 5 per cent lower than previously expected.

Wics chief executive Alan Sutherland said: “Scottish Water’s performance is encouraging and suggests that the clear incentive framework that is in place to regulate the public sector water industry has served the interests of customers well.

“However, this does not mean that we can be complacent, and we must continue to ensure that the industry is properly equipped to meet the challenges that lie ahead.”

Scottish water chief executive Douglas Millican the performance over the last five years represented a “major step forward” for the company, but he admitted “we cannot afford to be complacent”.

He said there is a “constant drive” for the company to deliver further improvements to drinking water quality, customer service, and environmental performance.