Deficit irrigation and increasing irrigation application efficiency were analysed as water-utilisation strategies through chance-constrained linear programming (CCLP) to establish whether these strategies were economically advantageous and water conserving. Deficit irrigation was modelled through scaling functions in the CCLP model, and potential return flow was calculated from optimal water application efficiencies. Results showed that increasing water application efficiency may be economically beneficial; however, the illusion might be created that water was conserved, while potential return flow was reduced. Deficit irrigation conserves water because water consumption decreases more than potential return flow. Deficit irrigation was economically advantageous only if larger areas are irrigated with the conserved water. Both strategies had substantial economic advantages if larger areas were irrigated with conserved water, but they did exert more pressure on streamflow levels. Before policies can be formulated that are of social importance, more information is required with regard to the mutual interaction among water legislation, water policy administration, technology, hydrology and human value systems.