Scottish Water workers represented by two unions have overwhelmingly backed strike action in light of a pay dispute.
Eighty-six per cent of GMB Scotland members who work at the publicly-owned facility backed industrial action.
Meanwhile, 89% of Unite members working for Scottish Water voted in favour of strike action.
GMB Scotland announced its ballot had revealed overwhelming support for action after executives were accused of riding roughshod over procedures for negotiating with staff.
Claire Greer, GMB Scotland organiser, said: "The overwhelming support for industrial action and the strength of feeling among staff about the conduct of senior management is no surprise.
"The way the company has allowed this situation to arise and then deteriorate so badly has been inept and needlessly antagonistic.
"It has only created distrust and conflict and now threatens disruption that could, with a good sense and better judgment, have easily been avoided.
"The solution to this could not be clearer. The pay offer must be decoupled from the wider restructuring of grades and salaries.
"We are happy to discuss both, but separately."
Talks with trade unions and the company at conciliation service Acas ended without any resolution on Monday, although but both sides agreed to resume discussions next week.
The unions will give Scottish Water two weeks' notice of strikes if there is no agreement made.
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The ballot result comes as Alex Plant, the new chief executive of Scottish Water, has come under fire for earning a reported annual salary of £295,000 in breach of the Scottish Government's public sector pay rules.
Mr Plant's salary is £25,000 higher than his direct predecessor despite the pay policy expecting a 10% reduction in the remuneration package.
The unions have accused the publicly-owned firm of acting like a "rogue employer" after combining an annual pay offer with a restructuring of salaries and grades, which, they say, will limit the wages of many lower-paid workers in the years ahead.
Members across both unions include waste water operatives, water treatment and burst repair operatives, maintenance engineers, electricians and sewage tanker drivers.
Unite general secretary Sharon Graham, said: "Scottish Water has got nobody to blame but itself for the mess it has created. It has refused to make our 500-strong membership a fair pay offer.
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"Instead, the boardroom has found the time to award its new chief executive an eye-watering pay package.
"Unite fully support members in the fight for better jobs, pay and conditions at Scottish Water."
Due to the frontline roles undertaken by employees in sewers, water treatment centres and on pipework, both unions believe strike action will directly impair Scottish Water's ability to respond to water leakages, flooding, pollution and quality concerns.
Stephen Deans, Unite regional coordinating officer, added: "Scottish Water has refused to meaningfully engage with us on pay and over a proposed new grading structure.
"Unite's membership includes key frontline workers and without them Scotland's ability to respond to any crisis stemming from waterworks, flooding and sewers is all but non-existent.
"Double standards have gripped the upper echelons of Scottish Water and we will not let this go unopposed.
"Strike action is now inevitable unless Scottish Water make a reasonable pay offer for 2023 which is separate from negotiations on a new pay and grading structure."
A Scottish Water spokesperson previously said: "We continue to seek negotiations with trade unions over a very fair and reasonable proposal to increase every employee's pay by at least 8% and modernise our pay structure in a way that our colleagues are demanding."
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