A School Day Without an Empty Tap: Sizing a Gravity Handwashing Station and Its Refill Schedule

This study examines a practical question in everyday hygiene by explicit arithmetic from stated assumptions. Daily demand was 259.0 litres, and with the reserve the required capacity was 297.8 litres, so the 25 litre container was selected and the 20 litre container rejected as 277.8 litres short. The 4 mm outlet delivered the target wash in 20 seconds at the stated head. One midday top-up of 10 litres, or 1 bucket trips, kept the level above the reserve line at every checkpoint in the simulated day, while a fill-once routine reached the reserve line at 13:10 and would have run dry before the last washing period on a day with visitors. Annual soap consumption at the station, at the small-dose rate, was 246.2 litres. The proposed arrangement is as follows. The station proposed pairs the sized container with a small outlet that makes each wash self-limiting, a marked reserve line visible to the monitor pupil or teacher, and a single scheduled top-up at the midday break. Demand is computed per wash and per day so any school can rescale the design by its own roll and washing frequency. All results are derived from the accompanying simulation script, in which every assumption appears as a named, replaceable value. SIMULATED, NOT MEASURED.