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(1)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 ([email protected]) **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. Residential Water Use (l/capita/day). 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$10,000 GDPPPP per capita). Above this level, the water demand has no relation with economy, and some countries with higher GDP levels have lower water demand. For example, the residential water use per capita per day in Tokyo is 249 L/d/person, that in Singapore is 167 L/d/person, and that in New York is 466 L/d/person, though they have small economic difference. Only economic factors hardly explain the water demand in developed countries. To predict future water demand in the world, it is important to estimate potential needs to which developing countries will reach when their economies grow above the critical level. 800. 600. 400. 200. 0 0. 10,000. 20,000. 30,000. GDPPPP per capita ($/capita/year) Source: World Bank, World Resources Figure 1 Economic Condition and Residential Water Use.

(2) To clarify the reasons that caused the differences of the residential water demand in developed countries, we investigated the residential water use for various activities, such as toilet flushing, bathing, laundry, cooking and others, and analyzed the important and contributing factors by activity. The investigated factors include geographic, economic and social aspects, such as climate, water price, and cultural background. RESIDENTIAL WATER USE IN DEVELOPED COUNTRIES Residential water use for each household activity We selected some cities (table 1) in developed countries and collected information on the residential water use per capita by households activities; toilet flushing, bath & shower, laundry, cooking (including drinking and washing dishes), and others. Total amount of residential water use in North America, Japan, and Australia are larger than those in European cities and Singapore, and the amount for each activity varies by city (figure 2). We analyzed these data by activity to clarify the reasons causing these differences, and which factor is the key to influence the cities’ water demand. Key factors to influence the cities’ residential water demand The following factors were thought to have influence on residential water use pattern; •Water resources We calculated cities’ annual water resources per capita by river basin. This factor indicates the abundance of water resources. It is assumed that people living in the city without enough water resources tend not to waste water, and their municipality take a lead to introduce technologies to save water (such as low flush toilet). Water resources are expected to influence the amount of water use for all activities. Table 1 List of Cities. Country USA. Canada Australia Japan. Singapore UK Austria Germany Netherland Switzerland France Finland Sweden Czech. City Servey Year Atlanta 1997 Waterloo/Cambridge 1999 Seattle 1999 Tampa 1999 Lompoc 1999 Eugene 1999 Boulder 1999 San Diego 1999 Denver 1999 Phoenix 1999 Scottsdale/Tempe 1999 Walnut Valley Water District 1999 Las Virgenes Water District 1999 Winnipeg 2001 Melbourne 2002 Tokyo 1997 Osaka 2001 Kobe 1990 Fukuoka 1997 Singapore 1995 East Anglian Region 1993 Vienna 1995 Hamburg 2002 Amsterdam 2001 Zurich 1997 France Total 2001 Helsinki 2001 Stockholm 2001 Prague 2001.

(3) 350. Toilet. Bath&Shower. Laundry. Cooking. Others. Water Consumption (l/capita/day). 300. 250. 200. 150. 100. Prague. Stockholm. France. Helsinki. Zurich. Amsterdam. Hamburg. Vienna. East Anglian(UK). Singapore. Fukuoka. Kobe. Osaka. Tokyo. Melbourne. Winnipeg. Walnut Valley WD. Las Virgenes MWD. Scottsdale/Tempe. Phoenix,. Denver. San Diego. Boulder. Eugene. Lompoc. Tampa. Seattle. Atlanta. 0. Waterloo/Cambridge. 50. Figure 2 Residential Water Use for each activity in various cities In case of cities in USA, only water for dishwasher is included in cooking. Water for preparation for food and drinking is included in others. In addition, water for gardening is excluded from total amount.. •Water price This factor includes not only water price but also sewerage price, because most of cities charged sewerage treatment fee according to the amount of water used. To compare water price among different countries and different currencies, we standardized water price by average income. Standardized water price = (Water & sewerage price / m3) / (Average income/capita/year) It is assumed that high water price makes people use water efficiently. Water price is can influence the amount of water use for bath, laundry and cooking. •Family size This means average number of persons in one household. It is assumed that large families can save water because of scale merit. Family size is possible to influence the amount of water use for laundry and cooking. •Climate Annual rainfall and average temperature represent the characteristic of cities’ climate. AS Climate relates to lifestyle, it is possible to influence the amount of water use for all activities. •Dietary Culture To compare the dietary culture and customs, we consider the intake calories from staple food (rice or wheat). This factor is thought to relate to the amount of water use for cooking.. Analysis of key factors by household activities We analyze and select the factors influence water use pattern using multiple regression analysis..

(4) Water Consumption (l/capita/day). 140 120. Toilet Leak Toilet. 100 80 60 40. Figure 3 Water Use for Toilet. Toilet flushing Water resources could explain the amount of water for toilet flushing (figure 3, 4); Toilet flushing = 53.4 * Log (water resources) - 129.5 R = 0.78 Toilet flushing : l/capita/day Water resources : 106m3/year. Water for toilet (l/capita/day). 120 100 80 60 40 20 0 3. 3.5 4 LOG(Water Resources) Figure 4 Water Resources and Water for Toilet. 4.5. Prague. Stockholm. Helsinki. France. Zurich. Amsterdam. Hamburg. Vienna. Singapore. East Anglian(UK). Fukuoka. Kobe. Osaka. Tokyo. Melbourne. Winnipeg. Walnut Valley WD. Las Virgenes MWD. Scottsdale/Tempe. Denver. Phoenix. San Diego. Boulder. Eugene. Lompoc. Tampa. Seattle. Atlanta. 0. Waterloo/Cambridge. 20.

(5) It is assumed that the less water resources result in the more introduction of low flush toilet (technological development). For the least amount example, Fukuoka municipality decided to introduce low flush toilet (less than 10L per flush) after water shortage in 1977 and now 6L per flush toilet began to spread. In Singapore, the second least amount, government commenced to install low flush toilet (4.5L per flush) to public housing instead of ordinary toilet (9L per flush) in 1992, and decided to install it to all of the new and on-going projects by law from 1997. In addition to the amount for toilet flushing, we have to consider toilet leak. Toilet leak indicates the trickling water to avoid water pipe from freezing. Cities where the temperature goes lower than -10 degrees centigrade need to include water for toilet leak as the climate factor. Bath and shower We could find no factor which influenced the amount of water for bath and shower. By comparing the amount, we can classify cities to four groups; North America, Asia, Western Europe and Northern & Eastern Europe (figure 5). However, we could not clarify the reasons causing difference of these groups. Laundry Water resources and water price could explain the amount of water for laundry (figure 6, 7, 8);. 80. 60. 40. Prague. Stockholm. Helsinki. France. Zurich. Hamburg. Amsterdam. Vienna. East Anglian(UK). Fukuoka. Singapore. Kobe. Osaka. Tokyo. Winnipeg. Melbourne. Las Virgenes MWD. Walnut Valley WD. Scottsdale/Tempe. Denver. Phoenix. San Diego. Boulder. Eugene. Lompoc. Tampa. Atlanta. 0. Seattle. 20. Waterloo/Cambridge. Water Consumption (l/person/day). 100. Figure 5 Water Use for Bath and Shower. Laundry = -0. 079* Water price +21.9* Log (Water resource) -25.8 Standardized beta Water price: -0.626, Water Resource: 0.420 Adjusted R square = 0.684 Laundry : l/capita/day Water price : (capita*year* 106)/m3 Water resources : 106m3/year. If people reduce the number of times to wash clothes and wash more clothes together, the amount of water for laundry can be reduced. We assumed that water price made people reduce the number from economical point of view, and similarly the lack of water resources did from mental (conscious for saving water) point of view..

(6) Water for Laundry (l/capita/day). Water for Laundry (l/capita/day). 70 60 50 40 30 20 10. 70 60 50 40 30 20 10 0. 0 0. 50. 100 150 Water Price. 200. 3. 250. 3.5 4 LOG(Water Resources). 4.5. Figure 8 Water Resources and Water for Laundry. Figure 7 Water Price and Water for Laundry. Cooking Because the data for cooking in USA and Canada was included in other uses, we omitted them and analyzed the cities in Europe, Asia and Oceania only. Water price could explain the amount of water for cooking (figure 9, 10); Cooking = 2,049 * 1/ Water price +4.73 R = 0.760 Cooking : l/capita/day Water price : (capita*year* 106)/m3 In addition, there is some possibility of that type of staple food influences the amount of water for cooking. Rice eater tended to use more water than wheat eater, because rice is so sticky that we need more water for dish washing (figure 11). Figure 9 Water Use for Cooking Water for Cooking & Drinking (l/capita/day). 60. 50. 40. 30. 20. 10. 0 0.000. 0.005. 0.010. 0.015. 1/Water&Sewerage Price. 0.020. 0.025.

(7) Water for Cooking (l/capita/day) 50. 40. 30. 20. 10. Water for Cooking(l/capita/day). Water Consumption (l/capita/day). 0. 200. 400. 0. Wheat Calory (cal/capita/day). 600. 800. 60 Cooking-Wheat Calory. 0. 200. 400. As a result, key factors influencing each residential activity are determined as figure 12.. 600. Rice Calory (cal/capita/day). Helsinki Stockholm Prague. Helsinki Stockholm Prague. France. Zurich Zurich France. Hamburg Amsterdam. Hamburg Amsterdam. Vienna. Vienna. Fukuoka. East Anglian(UK). Kobe Fukuoka. Kobe. East Anglian(UK). Osaka. Osaka. Singapore. Tokyo. Tokyo. Singapore. Winnipeg Melbourne. Winnipeg. Las Virgenes MWD. Las Virgenes MWD. Melbourne. Walnut Valley WD. Denver. Denver. Walnut Valley WD. San Diego. San Diego. Phoenix. Boulder. Boulder. Scottsdale/Tempe. Eugene. Eugene. Phoenix. Lompoc. Lompoc. Scottsdale/Tempe. Tampa. Tampa. 0. Seattle. 20. Seattle. 40. Atlanta. 60. Waterloo/Cambridge. 80. Atlanta. 0. Waterloo/Cambridge. Water Consumption (l/capita/day) 60. 40. 20. Figure 10 Water Price and Water for Cooking. 60 Cooking-Rice Calory. 50. 40. 30. 20. 10. 0. 800.

(8) Water Resources. 0.780. Residential Water Use Toilet. 0.420 Water Price. Bath & Shower. -0.626 Laundry. Climate. 0.760. Dietary Culture Household Size. Cooking. Others Figure 12 key factors. influencing each residential activity. CONCLUSION The detailed estimation of residential water use could be analyzed by each activity, and we could find that the geographical (water resources and climate), political (water price) and cultural (dietary culture) factors were important in the cities of developed countries. In addition to the factors which we examined in this report, we could think some factors influencing water use, such as water pressure, number of people who usually stay in home, variety of dietary habitat, and so on. 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. Bibliography AWWA Research Foundation (1999), Residential End Uses of Water Edwards, K., and Martin L. (1995), Methodology for Surveying Residential Water Consumption, Journal of the Institution of Water and Environment Management, 9(5), 477-488 FAOSTAT (arranged by Dr. Yanagishima and Dr, Matsumura) Oki, T., Agata Y., Kanae S., Saruhashi, T., Yang, D. and Musiake, K. (2001), Global assessment of current water resources using total runoff integrating pathways. Hydrological Science Journal, 46, 983-995 Oki, T. and Sud Y.C. (1998), Design of Total Runoff Integrating Pathways (TRIP) - A global river channel network. Earth Interactions, 2 World Bank and World Resources Institute (2000-2001), A guide to world resources 2000-2001: people and ecosystems: the fraying web of life/United Nations. Development Programme, United Nations. Environment Programme, World Bank Online Database Yamanishi, O. and Manabe, H. (2002), Amount of water use by residential activity, Summary of the 46th Conference of Japan Water Association’s Kansai Branch, 61-64 (in Japanese).

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