Arcadis and Southern Water (SW) worked together to deliver a commercial and procurement transformation for its construction and maintenance supply-chains. The objective was to secure >20% efficiencies against a £multi-bn programme, and remedy legacy supply chain relationship issues. Through innovative commercial models and cultural change, we secured contractual commitment to shared targets with 6 leading industry contractors. Overall, a suite of improvements has been implemented which outperforms the efficiency target by 30%. Via a carefully structured, collaborative and evidence-based approach, relationships have also been transformed, supporting SW’s vision of a resilient and affordable water future for the South East.