Effects of water tariff structures on water demand in Tokyo metropolis

As the socio-economic structure of Tokyo has changed over the last few decades, the water demand also has changed significantly. The bulk customers who use larger amounts of water gradually diminish, and the number of single and small households has increased dramatically. Analysis of the impact of such changes is necessary to give a clearer idea on the future water demand. In this paper, the effects of water tariff revision in 1994 on water consumption were analysed. Using the data obtained from Tokyo Metropolitan Waterworks, it was proved that the total annual water consumption after the change of water tariff structure in 1994 decreased significantly compared to the preceding years. The decreasing trend, however, started two years before the water tariff revision, which coincides with the downturn of the Japanese economy. In order to further analyse the contribution of customers classified by monthly water consumption, the numbers of customers in all water consumption classes were analysed for the years 1994 and 2001. The analysis on changes of the numbers of customers in each water consumption class revealed that the most significant reduction in water consumption took place in a water consumption class IV (31–100 m³/month), which comprises small businesses and large families. The reduction of water consumption by bulk customers with monthly water uses greater than 100 m³ was not so significant. The reduction in water consumption by medium to large users was partly augmented by the increasing number of single and small family users.