The claim that ChatGPT consumes a 500ml bottle of water for every 10 to 50 responses originated from a modelled GPT-3 scenario, not a universal measurement. The figure came from research by Pengfei Li, Jianyi Yang, Mohammad A. Islam and Shaolei Ren, first released as a preprint in 2023 and later published in Communications of the ACM. They estimated direct freshwater consumption of about 700,000 litres for GPT-3 training in Microsoft’s US data centres, and offered the inference that GPT-3 or ChatGPT could consume a 500ml bottle of water for roughly 10 to 50 medium-length responses, depending on where and when the system was deployed. The number was a scenario estimate based on assumptions about energy demand, data-centre cooling and water used to generate electricity. Changing the model, hardware, location, season, cooling system or power supply changes the answer. Data-centre water figures combine direct water use at the facility, such as evaporative cooling, and indirect water use from electricity generation. A distinction also exists between withdrawal, water taken from a supply, and consumption. There is no universal amount of water consumed by a prompt.