Effect of the Cleanliness of Spray Nozzle on the Concentration of Microorganisms in the Spray Water in Warm-Water Bidet Toilet Seats.

Bidet-toilets are widely used in households and public spaces in Japan. The effect of nozzle cleanliness on spray water quality of warm-water bidet toilet seats is unknown. We conducted a long-term experimental model-based study (2015-2016) and two survey-based studies (A: 2018-2019 and B: 2020-2021) at a university campus. Survey A measured the effect of nozzle cleansing on total viable count (TVC) and heterotrophic plate counts (HPCs) in spray water. Survey B measured the total organic carbon, residual chlorine concentration, TVC, and HPC of different fractions of sprayed water. We found no upstream migration of microbes from the nozzle to water tanks. While daily cleaning of the nozzle surface could reduce bacterial count in spray water, continuous discharge of water washed away bacterial contamination. Fecal indicator bacteria were in traces in spray water, indicating proper maintenance of these toilet seats.