The line-up for the Essex & Suffolk Water scheme is Sir Robert McAlpine, Blackwell, Carillion, Costain, Birse, Laing O'Rourke and BM Nuttall.
Bids are due back early in July, with work on site likely to begin either towards the back end of this year or early in 2010.
The job involves increasing the capacity of the 21km-long reservoir by raising its level by 3.2m.
