Nicholas Jamison

While 0°C is the standard answer, it's not always true. This value is for pure water under standard pressure. Two key factors can change the freezing point:1. Impurities (Salt/Sugar): When you dissolve a substance like salt or sugar in water, you create a solution. The dissolved particles interfere with the formation of the rigid crystalline structure of ice. This lowers the freezing point. This is why we salt roads in winter—to prevent ice from forming even when the air temperature is below 0°C. Seawater, which contains salt, freezes at around -2 °C.2. Pressure: Increasing pressure generally lowers the freezing point of water, but only very slightly. It takes a tremendous amount of pressure to change it by even a single degree. This is why the effect of pressure is often negligible for everyday situations, but it is a critical factor in certain geological and engineering contexts.So, for your glass of tap water, it's 0°C. For ocean water or a brine solution, it's lower.