WHAM (Windermere Humic-Aqueous Model) is designed to calculate equilibrium chemical speciation in surface and ground waters, sediments and soils. The model is especially suitable for problems where the chemical speciation is dominated by organic matter (humic substances). WHAM combines Humic Ion-Binding Model V with a simple inorganic speciation code for aqueous solutions. Precipitation of aluminium and iron oxides, cation-exchange on an idealized clay mineral, and adsorption-desorption reactions of fulvic acid are also taken into account. The importance of ion accumulation in the diffuse layers surrounding the humic molecules is emphasized. Model calculations are performed with a BASIC computer code running on a Personal Computer.