A referendum resulted in 71 per cent of those taking part voting in favour of the partnership agreement. Thames Water has 5,200 employees.
Personnel director Julia Cherrett said other initiatives due to be introduced as a result of the agreement include a review of terms and conditions and improved training.
She said, “We and the trade unions see the agreement as the best way of enabling organisational change and ensuring that employees are properly involved and consulted about matters that affect them.”
Discussions about the partnership with unions Unison, GMB, AEEU and TGWU began early in the year.
The referendum, managed by the Electoral Reform Society, was then held between 17 July and 4 August.
The partnership is due to be implemented over the next few weeks with the first initiatives expected by next April.