Rate constants are presented for diffusion in dilute nonideal solutions with or without the presence of a spatially varying potential field. Expressions for the rate constants have been derived by earlier workers, and essentially the same derivation is reviewed and expanded in this paper to justify the expressions used for the rate constants. The diffusion rate constants are used in a random walker model to demonstrate how solution nonidealities can be captured accurately using this approach. Examples are presented of ideal solute diffusion as well as nonideal diffusion of nonelectrolytes and simple electrolytes in water. The use of the approach to simulate advection is described, and a possible strategy for extending the approach to more concentrated solutions is briefly discussed.