Abstract A range-adjusted measure (RAM) of efficiency, as recently developed in data envelopment analysis (DEA), is used to evaluate the performance of entities that supply water services in Japan. Its robustness properties are tested and pointed up for uses in improved accountability, and are further pointed up in terms of the potential for help in conducting performance and efficiency audits. The results from DEA are also joined with the Mann–Whitney rank order statistic to show how the two techniques may be jointly used in addressing issues of general policy. The Kanto Region and Kanagawa Prefecture in Japan are used for an illustration.