If the kettle is clean and dry, you pour water as soon as removed from the heat source, filled up to the brim, it will be potable for at least 2–3 days.

In the context of 2026 health guidelines (such as those from the NHS), water that has been boiled in a kettle is considered "sterile" enough for preparing baby formula only if it is used while still very hot—specifically, it should cool for no longer than 30 minutes so that the temperature remains above 70°C (158°F). This high temperature is necessary to kill any potential bacteria (like Cronobacter sakazakii) that might be present in the powdered formula itself. If you are simply talking about drinking water, once the water in the kettle cools to room temperature and is exposed to the air, it is no longer strictly "sterile," though it remains safe to drink for about 24 hours if kept covered. For medical or infant use, always re-boil the kettle if the water has been sitting for more than half an hour to ensure absolute safety.