Hundreds of staff at the nation's state-owned water supplier which has been at the centre of a row over executive pay are to strike from Friday after last ditched talks failed to reach a resolution.

The four-day strike is part of a rolling programme of industrial action which union leaders say threatens to disrupt emergency repairs, testing and maintenance.

It comes amidst a row, revealed by the Herald over the pay of three executives including bonuses of nearly £1m in the past five years despite the Scottish Government's public sector pay policy rules maintaining a suspension of performance related bonuses for over seven years.

It comes as Scottish Water has been ordered to carry out an emergency clean-up of  tap water supplies after they were found to pose a "potential danger to human health".

The Drinking Water Quality Regulator for Scotland (DWQR), has served an enforcement notice on the state-owned company after uncovering a maintenance backlog.

Scottish Water said the notice refers to water in storage tanks for use when there is a water main burst.

The water company has had the same pay structure for 21 years and has been designing a new one, but unions GMB, Unite and Unison have voted to strike after lodging objections.

READ MORE: Nearly £1m in bonuses paid out to three Scottish Water execs

The union UNISON said the strike will have "serious implications for water and sewage services – emergency repairs will not be done, water quality checks will not take place and, if the public report problems with their water supply, sewage or drainage, they will not be dealt with while staff are on strike".

Union insiders feared that the talks were a delaying tactic to allow Scottish Water to prepare for any disruption caused by the strike.

Claire Greer, GMB Scotland organiser, said the strikes, overwhelmingly backed by 83% of members, could easily have been averted by Scottish Water long before last-ditch talks at conciliation service Acas collapsed in the early hours of Thursday morning.

She said: “It is impossible to underestimate how ineptly the company has handled what should have been a straightforward negotiation.

The Herald:

“It has managed to infuriate a committed workforce and drive them to strike action when the dispute could have easily been resolved months ago.

“Scottish Water has repeatedly been given a clear choice between doing the right thing and making the situation worse and has taken the wrong decision every single time.

“It’s actions over the last six months are a template for how to demoralise staff and demolish industrial relations.

“The priority is to resolve this dispute but then lessons must be learned.”

Ms Greer, who had written to the First Minister urging him to intervene, said Scottish Water could easily have stopped the strikes by halting its attempt to make this year’s pay offer dependent on the imposition of a new salary structure without negotiation.

Unions say the dispute comes after managers suddenly linked this year’s pay offer to a wider restructuring of grades and salaries which, unions say, will limit future wages and must be negotiated separately.

UNISON said the new pay and grading proposal that will see the earnings of their lowest paid staff drop by up to £5000. It says the proposals will cause years of wrangling over pay grades and push the lowest paid onto even lower wages and cause significant problems around equality legislation

The Scottish Government has defended the payment of nearly £1m in bonuses over five years on top of six-figure salaries having approved the bonus payments and revealed Scottish Water had a longstanding exemption from the rules. The First Minister insisted that they were aligned with public sector pay rules, which state that "we need to attract and retain highly experienced personnel to run vital public services".

Scottish Water has been looking at minimising disruption if strikes go ahead.

The Herald: Scottish Water

It said it has plans in place to protect essential services for customers ahead of industrial action.

A senior management team has been looking at all areas of Scottish Water activity that may be impacted by the strikes led by members of Unison, Unite and GMB Scotland.

It has previously said their offer is "fair and reasonable" and would mean an 8% rise in pay for every staff member alongside a pay and grading structure reform.

But unions say the pay needs to be split from the reform which they believe will have long-term impact on workers’ pay and should be subject to separate negotiations.

UNISON Scottish Water branch secretary Patricia McArthur said: “Strike action is always a last resort, but Scottish Water managers are imposing a new pay structure with no involvement from staff, which is not acceptable. It is storing up problems for the future.

READ MORE: Why ScotGov-owned bodies are at the centre of a pay rules row

“It seems that Scottish government’s Fair Work and equality commitments don’t matter in our biggest and most precious public asset. We need urgent intervention from the Scottish government to talk with unions and get meaningful talks started.”

UNISON regional organiser Emma Phillips added: “Scottish Water truly are a rogue employer. Our strong ballot result shows the strength of feeling among our members, who have overwhelmingly rejected the employer’s slap dash proposals.

“Despite this, Scottish Water are insisting they are still going to implement the changes to employment contracts and pay structures.

“Scottish Water is ripping up the government’s fair work and equality guidance and it’s just not good enough – our members deserve better.

“If the Scottish government don’t intervene, then they have been warned that they are storing up problems over pay structures and future equal pay. Re-grading has to be done properly with the full involvement of staff and unions.”

Scottish Water chief operating officer Peter Farrer said: “We regret that the unions have decided to take industrial action. Scottish Water remains committed to reaching an agreement with our unions that avoids industrial action. This has been the case throughout the negotiations over the proposal to modernise a 21-year-old pay and grading structure and provide employees with an in-year award of at least 8% for all.

“We will do all we can to ensure customers do not experience any disruption to their water supplies and that treatment of the country’s waste water continues as usual, despite the industrial action.

“A reliable water source is vital for everyone. Maintaining public health and protecting the environment are our priorities and it is the responsible course of action for us to have contingency plans ready. We are committed to maintaining our high levels of customer service during this dispute and are confident that those staff members who do not strike will be ready, willing and able to help ensure we do so.

“We are dismayed the unions have taken this course of action over what, at 8% or more for all, is an exceptional proposal for our people and one of the best in the public sector.”

Customer service general manager Kevin Roy added: “It is essential we can continue to provide customers with the high standard of service they have come to expect from Scottish Water. We have looked in detail at how our vast range of activities might be impacted by this action and have put measures in place to minimise any disruption.

“Among the work we are doing ahead of the strikes is the development of the Scottish Water website to provide customers with information on how we will be continuing to support their essential services.”