Crop restriction is often practiced in conjunction with wastewater treatment so that lower quality effluents can be used to irrigate non-vegetable crops (see table 3). Although this appears straightforward, in practice it is often difficult to enforce. It can only be done effectively where a public body controls the use of wastewater and laws providing for crop restricted are strictly enforced, where there is adequate demand for the crops allowed under crop restrictions and where there is little market pressure in favor of excluded crops (i.e. salad and other crops eaten uncooked). Crop restriction requires much less costly wastewater treatment and may be favored for this reason alone (but wastewater treatment engineers need to discuss this clearly with the appropriate regulatory agency and local farmers).