The potential-pH-temperature relationships for the aluminium-water system have been calculated by the methods of de Bethune, Khodakovskiy, Criss and Cobble, and Helgeson and a critical comparison made. The Criss and Cobble method produced the most consistent results and was used to construct a corrosion diagram for the range 25-300�C. The effect of the hydrolysed ions Al(OH)2+, Al(OH)2+ and Al(OH)30 was also calculated. The work has shown up a temperature effect which should be taken into account when designing and operating aluminium circuits in which different parts are operated at different temperatures.