Based on the use of thermodynamic data, chemical modelling offers a unique technique to predict and understand the behaviour of aluminium in aquatic systems. In this paper we describe the necessary precautions that must be taken to evaluate these thermodynamic data with the highest accuracy possible. The review is mainly concerned with the practical side of equilibrium studies and it puts a certain emphasis on the need for an unbroken chain from accurate solution preparation, via high quality measurements, to an unbiased data evaluation. In the paper we also discuss how these thermodynamic data change with changes in ionic strength and temperature.