Utility company Thames Water has indicated that it plans to cut its staff levels by 25 per cent over the next four years.
The GMB union has said it will fight front-line job cuts, but the company, which employs about 6,000 staff, has said it intends to keep compulsory redundancies to a minimum.
In an email to staff, Thames Water chief executive Jeremy Pelczer said that the job losses would help the firm to "be more efficient that its competitors", as well as securing its "long-term future".
"I have to guard against any complacency, towards customer service or efficiency, that may arise because we are a monopoly," he added.
"As we seek to drive the efficiencies needed to meet our goals, some of them will come through smarter procurement but some will come from different ways of working which will involve job cuts."
About 300 people will lose their jobs every year until the next decade, Mr Pelczer explained.
Thames Water, which is owned by German parent company RWE, has consistently been criticised for failing to meet water leakage targets, which have been set against the backdrop of drought conditions in Britain and the summer heatwave.