Water utilities provide an essential service of delivery of clean and safe drinking water to society. As migrations to cities increase, the demands on water utilities are increasing. Traditionally optimisation was focused on the reduction of energy demand and water losses of the water distribution network (WDN), but contemporary networks are integrated, and optimisation is not limited to the WDN. In the current landscape, business sustainability is paramount. Sustainability is inclusive of the economic, environmental and social performance of the business. This study develops an approach to determine the sustainability performance of a water utility, defined as the Business Performance Index (BPI). The BPI is a function of a water utilities key performance indicators of energy demand, water volume entering the WDN, cost and execution time. The approach (1) quantifies the BPI based on current operational practice, (2) allows the business to set a target BPI and (3) identifies the business operational parameters to achieve the target BPI. The approach is demonstrated by application to a metropolitan water utility, where target BPIs for time t1 and t2 are set at 5% and 8% lower than the quantified baseline BPI. The approach determines that the target BPIs are not always achievable given business constraints and interdependencies, hence a realisable BPI is defined. The realisable BPI at time t1 and t2 is 2.3% and 6.4% less than the baseline, respectively. For each of the realisable BPIs the required statuses of the operational variables are defined. The results further identify three key operational aspects for improvement, invoicing, business process energy demand and process energy demand. The approach and the defined BPI enables a water utility to optimise energy demand, water losses, cost and execution time, holistically, as the interdependencies are considered.