Building groups Galliford Try and Costain have won infrastructure contracts together worth more than £400m from privately owned water and waste utility Southern Water.Galliford said a joint venture part-owned by its infrastructure business had been appointed by Southern Water to work on infrastructure connected to its 2015-2020 AMP 6 investment programme.The contract, which is expected to be worth about £215m, will run from 2015 to 2020 and could be extended a further five years to 2025.Galliford chief executive Greg Fitzgerald said: "We are delighted to have secured such a substantial amount of long-term business. We look forward to working again with Southern Water and bringing the benefit of our experience of collaboration across the UK water sector to the company and its customers."Costain said its joint venture with MWH had won a similar deal worth about £200m.Costain chief executive Andrew Wyllie said: ""We are delighted to have been re-appointed to Southern Water's AMP framework and look forward to working with the company and its other partners."Shares in Galliford were unchanged at 1236p and Costain lifted 3.25p or 1.1% to 289p at 08:42 in London.