Unison represents more than 1,000 workers at Scottish Water and had a 69% turnout, while 61% of GMB members voted and Unite said there was a “high turnout” of its 500 members.
Hundreds of Scottish Water staff have backed strike action in a pay dispute.
More than 60% of those voting at each union backed a strike – 65% at Unison, 67% at GMB and 71% at Unite – while more than 70% backed action short of a strike – at 73%, 67% and 80% respectively.
Unite general secretary Sharon Graham said: “Unite’s 500-strong membership at Scottish Water is angry at the double standards gripping the executives of the public body.
The GMB, Unite and Unison unions said their members voted for walkouts and action short of a strike such as an overtime ban.
