The £24m contract will cover planned mains replacement works for the water company’s 300,000 customers in Southern Hampshire and West Sussex.
Cappagh, which has built up a track record working for Thames Water in recent years, beat six firms to take the AMP6 infrastructure term service contract.
Civils and electrical contractor Durkin and Sons held the previous AMP5 contract in the region.
Fast-growing Cappagn, in joint venture with J Browne, also secured the AMP6 contract to provide sewerage network maintenance services across Southern Water’s entire region recently.