Five hundred jobs are being cut by the Coventry-based company Severn Trent Water.
The firm, which employs 6,000 people across the UK, said it was losing the roles from its management and support departments after merging its sewerage and water supply divisions.
It is unclear how many of the posts will go from its Coventry headquarters.
The firm said it would create up to 100 additional front-line roles and has no plans to make cuts in that area.