Tokyo – About 15% of municipalities in Japan are positive about replacing their existing sewer systems with combined septic tanks, according to a recent survey. The survey was conducted after a law revision was enacted during the last session of parliament to review a policy to expand sewer networks, in light of the cost of maintaining and renewing aging equipment. Sewer systems across the country are deteriorating, and many municipalities are burdened with maintenance and renewal costs as their populations shrink.
In January 2025, an underground sewer pipe collapsed in the city of Yashio, Saitama Prefecture, causing a large sinkhole to emerge. Following this incident, the law revision made it easier for municipalities to shift to combined septic tanks by allowing them to reduce or discontinue sewer systems. The survey asked 1,464 municipalities with populations under 100,000 about whether they were positive about switching to septic tanks as of July.
Of them, 692, or 47.3%, gave valid responses. Of the respondents, 105, or about 15.2%, said that they were positive about switching to septic tanks, including the town of Minamiizu, Shizuoka Prefecture, which had already done so. On the other hand, 406 municipalities answered that they did not currently see a need to replace sewers with septic tanks.
Some said that such a replacement would be practically difficult due to budget and personnel shortages.
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