A Full Wash on Two Litres: Sequencing a Sponge Bath to Minimise Water at a Stated Cleanliness Standard

This study examines a practical question in everyday hygiene by explicit arithmetic from stated assumptions. The optimised sequence used 2.6 litres in total, including cloth rinses, and met every zone standard. Top-to-bottom habit used 4.1 litres and generous basin changing by appearance used 5.5 litres, while an attempt to use a single basin throughout failed the standard for 3 zones. The optimised schedule needed 2 basin fills and 26 sponge passes in total, with the feet washed last from water already carrying 68 soil units, which the model permits because no cleaner zone follows them. Water per zone averaged 0.33 litres in the optimised schedule. The proposed arrangement is as follows. The proposed procedure washes zones in descending order of cleanliness requirement weighted by soil, reserves a small separate rinse vessel for the cloth, and changes the main basin on a soil budget rather than by appearance. The output is a one-page order of work that a carer or household member can follow without calculation. All results are derived from the accompanying simulation script, in which every assumption appears as a named, replaceable value. SIMULATED, NOT MEASURED.