This paper looks at energy management by pump scheduling using a software package called WATCHMAN1. The objective of pump scheduling is to supply demand at minimum operating cost while satisfying all operating constraints. This is achieved by choosing which sources and pumps to use, at what times and at what speed. Factors which affect cost include electricity tariff structure, pumpset efficiencies, marginal cost of treatment and the heads developed by the pumps. The constraining rules include allowable reservoir levels, pump availability, works throughput limitations and system pressure rules. For all but the simplest of system, it is a difficult task to find the true global optimum and satisfy all the operating rules. A case study shows how the software maximizes energy efficiency.