Abstract
Electric bidets have become widespread in Japan and are now rapidly being installed across the rest of Asia, the United States, and the European Union. However, the impact on water infrastructure has not yet been sufficiently evaluated. Using Japan as an example, we assess the impact of the spread of electric bidets on the existing water infrastructure and use the results to predict the impact in countries in which the spread of electric bidets is expected in the future. In this study, we first proposed a model of electric bidet use on the basis of the results of a questionnaire survey. In Japan, the frequency of electric bidet use is considered to be the same as that of toilet use, and this model is used by the Ministry of Economy, Trade and Industry (METI) in its official evaluation of equipment performance. However, in this survey, we found that 30–40% of respondents did not use electric bidets, even though they have become commonplace in Japan. The reason for this was a vague sense of anxiety about sanitation. Based on the results of the survey, the model for electric bidet use was set to once a day for men for flushing following defecation and once a day for women for either flushing following defecation or bidet flushing. This is considerably less frequent than the conventional Japanese electric bidet use model for women, which models for one flush following defecation and three flushes following urination. Japan’s Energy Conservation Law requires improved energy efficiency in 32 items of equipment, of which the electric bidet is one. Because of this regulation, the electricity consumption of electric bidets has decreased by one fourth in the past 10 years. When a new model representing actual usage was applied, the environmental impact of the electric bidets currently sold was shown to be minimal.
Highlights
By assessing the impact of water saving on the CO2 impact, we have shown that water saving contributes to the low-carbonization of cities [1,2,3,4]
We investigated the actual use of electric bidets through a questionnaire survey, modeled this, estimated their CO2 emissions, and compared them with the values already calculated in the Top Runner Program
We proposed an electric bidet use model by assigning information on whether an electric bidet is used following each of these elimination acts, which was obtained in this study
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The equipment selected for the Top Runner Program covers 32 items that have a large impact on CO2 emissions in Japan because of their large energy consumption and high diffusion rate [7]. To promote the reduction of CO2 emissions, the government is promoting a system to manage CO2 emissions derived from primary and secondary energy consumption at factories and business sites and supply chain emissions from the use of equipment manufactured and sold by such companies [8] In consideration of these trends, it will become increasingly important to quantitatively calculate the CO2 emissions of various equipment and facilities used in buildings. We investigated the actual use of electric bidets through a questionnaire survey, modeled this, estimated their CO2 emissions, and compared them with the values already calculated in the Top Runner Program. The evaluation of the impact of the electric bidet in this study will be helpful in determining whether they will have a negative impact on the trend of CO2 emission reduction in cities in regions in which they are becoming widespread
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