Water service disruption and emergency restoration following the 2026 Kumamoto earthquake

Abstract The 28 July 2026 Kumamoto earthquake (JMA magnitude Mj 7.1; seismic intensity 7 at Uki City and Hikawa Town) produced a peak water-main service disruption reported as about 108,000 households on the restoration-outlook decks and as about 108,100 households in the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) 51st damage report, across 14 municipalities. Official household counts are often reused as if they were pipe-break inventories. This paper’s contribution is methodological: a four-class protocol that keeps physical damage, service state, restoration action, and discovery time in separate columns; a locked closed-population denominator N0 = 108,000; a three-state last-mile reading of no-flow, restricted-flow, and mains-restored service; and a scenario-based first-week uncertainty interval on household-days rather than a single integral. About 59% of the locked peak had left the remaining-outage list by day 7 and about 90% by day 19; emergency restoration of damaged water mains was declared complete on day 31. Restricted flow covered about 16,500 households on 14–15 August. Sewerage is parallel evidence (282 km; eight sites; four later defects), not a second household series. Household-days of remaining headline outage over 31 days are 0.92, 0.97, and 1.10 million under three documented first-week scenarios (a scenario-based interval, not a mathematical bound on every monotone path). A piecewise-linear interpolation through official process-date anchors is used as an operational description of the ministry clock; it is not offered as a preferred recovery model. The matching two-state resilience index is 0.72, 0.71, and 0.67. Pipe-material repair rates are not estimated. Online Resource 1 is the authoritative numerical dataset for reproducibility and separates official, approximate and reconstructed integers.