Many of the active substances in black tea do not develop at temperatures lower than 90 °C (194 °F). As a result, black tea in the West is usually steeped in water near its boiling point, at around 99 °C (210 °F). The most common fault when making black tea is to use water at too low a temperature. Since boiling point drops with increasing altitude, it is difficult to brew black tea properly in mountainous areas. Warming the tea pot before steeping is critical at any elevation.