Residential water demand analysis by household activities Yurina Otaki*, Masahiro Otaki**, Toshiya Aramaki*** and Osamu Sakura**** *The University of Tokyo, Graduate School of Interdisciplinary Information Studies, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan (yurina@iii.u-tokyo.ac.jp ) **Ochanomizu University, Humanities and Science, 2-1-1 Otsuka, Bunkyo, Tokyo 112-8610, Japan ***Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8904, Japan ****The University of Tokyo, Interfaculty Initiative in Information Studies, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan ABSTRACT Sanitary water demand was defined as primary needs and the water for residential use would have to be increased for this requirement. However the world water resources are limited. Therefore, reasonable and accurate estimations of water demand are necessary. . In this paper, we investigated the factors which have influence on the residential water demand. We dividedly studied residential water use by household activities; toilet flushing, bath and shower, laundry, cooking and others, and we could find that the geographical (water resources and climate), political (water price) and cultural (dietary culture) factors influence to the residential water use for each activity in the cities of developed countries. When we predict the future water demand, we have to analyze two groups separately; If a country’s economy is below a certain level, the economic factors are the most important for the estimation. If its economy grows above a certain level, we have to use the analysis by each activity dividedly. KEYWORDS Residential water use, Household activities, Multi Regression Analysis, Water Resources, Water Price INTRODUCTION In the declaration of the Johannesburg Summit 2002, sanitary water demand was defined as primary needs and the water for residential use would have to be increased for this requirement. However the world water resources are limited. Therefore, reasonable and accurate estimations of water demand are necessary. . In this paper, we investigated the factors which have influence on the residential water demand. Figure 1 shows the relation between GDPPPP per capita and residential water use per capita per day by country. From this figure, we can see that the increase of residential water use is accompanied with the economic condition until the certain economic level (around US$10,000 GDPPPP per capita). Above this level, the water demand has no relation with economy, and some countries with higher GDP levels have lower water demand. For example, the residential water use per capita per day in Tokyo is 249 L/d/person, that in Singapore is 167 L/d/person, and that in New York is 466 L/d/person, though they have small economic difference. Only economic factors hardly explain the water demand in developed countries. To predict future water demand in the world, it is important to estimate potential needs to which developing countries will reach when their economies grow above the critical level. 0 200 400 600 800 0 10,000 20,000 30,000 GDPPPP per capita ($/capita/year) Residential Water Use (l/capita/day Figure 1 Economic Condition and Residential Water Use Source: World Bank, World Resources