Water Quality Indices as Tools for Decision Making and Management

Water Quality Indices (WQIs) are composite indicators of water quality that pool together otherwise complex water quality data into an aggregate value that can be quickly and easily communicated to its intended audience. These indices have been used to provide comparisons of water quality status for different locations and at different times, which is helpful in prioritizing management efforts and funds. These WQIs can also be used as tools to predict potentially harmful conditions. They are also potentially valuable in assessing and communicating overall impacts of existing, planned, or proposed water quality interventions and management decisions. This manuscript presents a primarily literature-based look at WQI potentials with regard to their use as tools for decision making and management. Illustrations using monitoring data are also presented to provide additional information and comparisons to literature-based determinations. Of the existing WQIs, objective index formulations offer more flexible options for application allowing incorporation of varying determinant sets to capture location-specific conditions and changing water quality concerns. Incorporation of expert opinion at some level is important for the acceptability of WQIs as tools in water resources management. The use of the indices on a continuous basis provides long-term data which is helpful for decision making and management.