Efficiency in the water industry

This paper considers the use of efficiency measurement in the regulation of the water industry in England, Wales, and Scotland. Ofwat employs econometric models; some examples of these are provided together with an explanation of the way Ofwat applies them to the financial model for each company. Finally we consider the question of the accuracy of these models and conclude that, while the models probably do contain information about companies' scope for cost reductions, Ofwat probably overestimates the quality of its models. Specifically Ofwat's estimate that 90% of the water model residuals and 80% of the sewerages models can be attributed to efficiency has not been given an explicit justification and probably overstates the case.