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Best practices for managing drainage water quality include the use of constructed wetlands for reducing nutrient loads. Nutrient reduction can be related to the hydraulic performance of a wetland. Hydraulic indexes used for quantifying the hydraulic efficiency of a wetland have more value when they can be used to predict treatment ability. This paper evaluates a number of common indexes describing hydraulic efficiency and relates them to the expected treatment derived from time dependant first order nutrient reductions. There is a need for a hydraulic index demonstrating strong correlation to pollutant reduction in order to identify the optimal wetland configuration for maximizing residence time. Such an index should quantify the effects of the various wetland parameters that influence the residence time distribution and supply the bounds for pollutant reduction.