The manual shift of residential wet appliances (dishwashers, washing machines and tumble dryers) in French households that have subscribed to a Time of Use (ToU) tariff represents a flexibility potential available already today and at zero-cost. To quantify this flexibility, a bottom-up model is here proposed and validated. This includes a stochastic occupant behaviour model for predicting the use of the wet appliances and an overlying agent-based model to predict their shifting under the ToU tariff. The model is validated using empirical data collected in a recent monitoring campaign, which provided energy measurements from 60 dishwashers, 100 washing machines and 23 tumble dryers in 107 French households for a period of 1 year.