The strategic solutions provider deal is understood to be worth £100m-£200m.

Just last week MWH was also named one of six delivery partners for Anglian Water’s  £1.3bn water and wastewater infrastructure programme.

The firm also landed a 10-year deal with Severn Trent as one of three consultants to support its AMP6 and 7 delivery programme late last year and the key programme manager  role in the Thames Super Alliance.

Under the latest deal, MWH’s main task will be to develop the most cost-efficient and sustainable options for meeting Southern Water’s  performance goals.

It will determine whether or not new build projects are necessarily the best solution, as well as supporting projects from definition up to and including outline design.

MWH will also directly oversee the work carried out by up to four design and build delivery partners for the AMP6 spending period.

This is presently out to tender and will be split between pipeline infrastructure and a separate arrangement for water, waste water and pumping station building works.

The successful contractors are due to be named in July.

Overall, Southern Water aims to invest around £3bn between 2015 and 2020, including refurbishment and upgrade work.