In this paper, a novel approach to measure equity among the polluters through a waste load allocation model is presented. The concept behind arriving at the proposed new equity measure is that a polluter may be penalized according to the amount of DO deficit that the polluter's waste load causes in a river within the reach, before other polluter's load joins. The waste load allocation model is developed as a multiobjective model with two objectives of treatment cost minimization and equity maximization. The developed model was applied to Thambraparni river in Tamil Nadu, India. Since the flow in the river varies from month to month, the monthly tradeoff curves between treatment levels versus equity have been presented. © 2010 by World Scientific Publishing Co. Pte. Ltd. All rights reserved.