Equity-sensitive utility planning for post-earthquake shelter sanitation under incomplete capacity evidence

Background Post-earthquake sanitation is an urban utility-continuity problem because water, waste handling, deployable equipment, and safe access jointly determine whether toilets can serve shelter occupants. Methods We combine an official prefectural snapshot of 81 open shelters and 3,585 evacuees with municipality screening and three residential-composition scenarios, then analyze 53 matched shelters in Kumamoto and Yatsushiro Cities. The framework separates observed occupancy and deployments from synthetic female and functional-support demand, accessible-unit parity screens, and conditional logistics. Findings Separate rounding at each shelter raises prolonged-stay requirements from 93 to 112 units in Yatsushiro and from 14 to 23 units in Kumamoto. In Yatsushiro, reported temporary toilets imply a 31-unit shortfall across 11 shelters; the shortfall reaches zero only under an upper-bound scenario that permits all 72 reported surplus units to move, of which 31 are transferred. Conclusions The results support targeted field verification, gender-responsive service packages, and conditional resource staging. They do not establish functional toilet capacity, accessible-toilet compliance, observed subgroup composition, or an optimal dispatch plan. Shelter sanitation policy should preserve site-level demand and verify utility and equipment operability before deployment.