By using tap water, a household consumes 2 eu of energy daily.

Energy is not always consumed in visible forms such as light, heat, and motion. There are many other ways in which we consume energy without realizing it. Water supply is one of them.

Water is supplied to our households after going through the following processes:
(1) Drawn from dams and other sources and pumped to a water purification plant;
(2) Filtered and disinfected with chemicals; and
(3) Pumped to each household.

Of course energy is consumed at each stage of this process.

Of the total energy spent on running the water supply system, the majority is consumed in the form of electricity required for pumping. The total electricity used for the water supply in Japan is about 7.9 billion kwh, which is a little less than the electricity generated by a one-million-kw-class nuclear power plant. Although this is not consumed solely by households, if we calculate the amount for a family of four, it is equivalent to keeping a 30w light bulb on. Moreover, if we include additional energy required for producing chemicals and other aspects of running the system, as well as energy initially needed for constructing purification plants and conduits, one cubic meter of tap water takes approximately 3,100 kcal. Assuming one person consumes 400 liters of tap water per day, a family of four consumes 4,960 kcal, that is, 2 eu. Even though this is no small amount, most people are unaware of the fact that they are consuming energy when using tap water.

Also, the sewage system requires energy. Similar processes as in the water supply-although in the opposite order-take place in the sewage system: constructing pipes; pumping waste water to a treatment facility; treat and release water. According to a statistics for Tokyo's 23 wards, more electricity is consumed in the sewage system than in the water supply.

Although the industrial use account for 46 percent of the Japan's total energy demand, the end users are in fact citizens. What is running from the tap is not only water but also energy. Saving water leads to conserving both resources and energy.

Most figures are as of 1995.
Statistics on Water Supply (FY 1995) (compiled by Japan Water Works Association and the Water Supply Division of the Ministry of Health and Welfare).
Figures are regarding waterworks and tap water supply and include the amount of unused water but exclude simplified and dedicated private waterworks. In 1995, a total of about 17 billion cubic meters of water was supplied to approximately 120 million people in Japan. 17 billion / 120 million / 366 days = approximately 0.4 cubic meters, or 400 liters.
Annual Report on Tokyo's Sewage System (FY 1995) , (published by the Tokyo Metropolitan Government's Bureau of Sewage).
Energy Conservation Handbook (Energy Conservation Center).

Test calculation of the life cycle energy of water supply: Water Supply in the Age of Global Environment , compiled by the Society of Water Supply and Global Environment, published by Gihodo. Figures are regarding water supply businesses that provide more than 30,000 cubic meters of water per day and include energy loss in power generation. This publication offers insight into unused energy related to urban water supply and sewage systems.

Electricity required for sewage treatment: The pumping stations and sewage facilities in Tokyo's 23 wards (population of about eight million) use a total of approximately 675 million kwh of electricity annually. In terms of the electricity consumption per family of four, this is equivalent to keeping a 40w light bulb on all the time. In the case where a small combined purification tank is installed, about 60 to 80w of electricity is constantly consumed. This tank does not require sewage pipes but maintenance must be provided by each household.