The TOXSWA model has been extended with the functionality to simulate hydrolysis and biotic transformation in water. TOXSWA simulates the fate of pesticides in water bodies to calculate exposure calculations for aquatic organisms or sediment-dwelling organisms as part of the aquatic risk assessment of pesticides. Hydrolysis and biotic transformation are modelled as first-order processes, occuring in the water phase only. The hydrolysis transformation rates are considered to be dependent on both pH and temperature. The biotic transformation rate is considered to be temperature-dependent only.