Can urban growth patterns take advantage of economies of scale in infrastructure by relying on fewer and larger treatment plants? Estimates of potential cost savings from alternative wastewater treatment consolidation strategies for the metropolitan Chicago region suggest that the timing of consolidation is important. Carefully timed consolidation, even consolidation that occurs after development has occurred, might yield present value savings on the order of $170 million in capital costs. These potential savings are large enough that such strategies should be considered when planning for metropolitan growth.