As Japan's Sewers Age, a Few Towns Consider Switching to Septic Tanks

According to a recent survey reported by The Japan Times, approximately 15% of responding municipalities in Japan are expressing a positive stance toward replacing their existing sewer systems with combined septic tanks. This shift in perspective comes as local governments grapple with aging infrastructure, shrinking local populations, and mounting financial burdens associated with maintaining and renewing underground pipelines.

The national conversation regarding sewage infrastructure shifted following a legislative change enacted during a previous session of parliament. Lawmakers moved to review a long-standing policy focused heavily on expanding sewer networks, primarily in response to the escalating costs of keeping aging equipment operational across the country.

Infrastructure deterioration poses a very real and visible threat to communities. A striking example occurred in January 2025 in the city of Yashio, located in Saitama Prefecture. In that incident, an underground sewer pipe suffered a major collapse, triggering the emergence of a large sinkhole directly into the urban landscape.

Following the Yashio incident and the subsequent legislative adjustments, the path for local governments has changed. The law revision made it legally and logistically easier for municipalities to transition away from centralized pipelines by allowing them to officially reduce or completely discontinue their traditional sewer systems in favor of decentralized alternatives.

To gauge the reaction of local governments to these policy shifts, a survey was conducted targeting municipalities with populations under 100,000. Out of 1,464 eligible local governments polled as of July, valid responses were received from 692 authorities, representing roughly 47.3% of the group.

The results of the survey highlight a growing, though still minority, openness to decentralized wastewater management. Specifically, 105 of the responding municipalities—accounting for about 15.2% of valid replies—stated that they were positive about the prospect of switching to combined septic tanks.

Among those already embracing the shift is the town of Minamiizu in Shizuoka Prefecture. According to the findings, Minamiizu has already completed the transition away from a traditional network, serving as an early adopter of the decentralized septic tank model under the evolving national framework.

However, widespread adoption across the country is far from guaranteed. A significant portion of local authorities remains unconvinced or unable to make the change. The survey revealed that 406 municipalities answered that they did not currently see a compelling need to replace their existing sewers with septic tanks.

Many of the hesitant local governments pointed to practical barriers preventing a swift transition. Respondents noted that replacing extensive sewer networks with septic systems would be practically difficult due to severe budget constraints and ongoing personnel shortages within municipal offices.

As Japan continues to navigate the pressures of demographic decline and aging public works, the debate over how best to manage wastewater safely and affordably remains open. While only a fraction of smaller towns are actively pursuing septic tanks, the legislative framework now provides a viable exit strategy for municipalities struggling to maintain aging underground infrastructure.