AMP4 contract guarantees work for five years and could be extended to ten.
A consortia led by Costain and United Utilities has won a £750m AMP4 contract with Southern Water.
The contract is part of Southern Water’s five-year quality and environmental capital investment programme worth £1.8bn.
The group says that it has secured 20% of the UK’s £16bn AMP4 expenditure programme over the next five years.
Stuart Doughty chief executive said: “This has given the company guaranteed earnings amounting to 50% of its forward order book for the next five years, renewable to ten.”
Costain and United Utilities have a 40% share in the joint venture while MWH hold the remaining 20%.