Estimating Water Demand under Increasing-Block Tariffs Using Aggregate Data and Proportions of Users per Block

The price specification suggested by Nordin (1976) for theanalysis of demand under block tariffs is applied to estimatewater demand functions using aggregate data from the Northwest ofSpain. The traditional way of using Nordin's specification whenonly aggregate data are available (using values of marginal priceand difference faced by the average user) is compared with thetheoretically correct one. The latter uses the average marginalprice and the average difference, these averages being weighted bythe proportion of users per block. The availability of data on theproportion of users per block permits also the explicit modellingof the choice of block. The results show that, in the sampleanalyzed, the values of price elasticity under the traditionalspecification and the more innovative one are not significantlydifferent.