A carbon footprint of drinking water pipes in Tokyo: exploring the neglected use phase

Purpose: The environmental impact of drinking water infrastructure is often assessed based on the environmental impact of piping material, while operational conditions such as leakage and pumping energy are neglected. This study quantifies the carbon footprint of the drinking water service pipes connecting distribution pipes to households in Tokyo, which transitioned entirely to stainless steel by 2004. It includes the impact of the production of pipes, repair, and their influence on the leakage rate.

Methods: This study presents a carbon footprint analysis of water pipes in Tokyo, encompassing production, use phase, water leakage, and repair scenarios both before and after the transition to stainless steel pipes. According to information from the water supply company, 90% of the leakage in the water system is attributable to the water service pipes. Through changing the pipe materials, the water leakage rate was reduced from 15 to ~ 3–4%.

Results and discussion: The shift to stainless steel likely reduced the carbon footprint by 7–9%, primarily due to lower leakage and thus fewer emissions from water treatment and pumping. Pipe production emissions are offset within ~ 25 years, yielding long-term savings. Despite material changes and reduced need to pump excess leaked water, total electricity demand for distribution slightly increased (1979–2021), most likely because of increased pressure in the entire system. The findings highlight that operational impacts, especially leakage rates, are a key parameter in determining the carbon emissions of drinking water pipes.

Conclusions: The results show that the carbon footprint of drinking water distribution is dominated by leakage from material deterioration, not by the carbon intensity of the piping material itself. Further research is needed to evaluate the generalizability of these results across diverse geological settings and drinking water sources.