A global Water Quality Index and hot-deck imputation of missing data

Water is an essential resource for life on Earth and available freshwater resources are emerging as a limiting factor not only in quantity but also in quality for human development and ecological stability in a growing number of locations. Water quality is a significant criterion in matching water demand and supply. Securing adequate freshwater quality for both human and ecological needs is thus an important aspect of integrated environmental management and sustainable development. The 2008 Environmental Performance Index (EPI) published by the Yale Center for Environmental Law and Policy (YCELP) and the Center for International Earth Science Information Network (CIESIN) at Columbia University includes a Water Quality Index (WATQI). The WATQI provides a first global effort at reporting and estimating water quality on the basis of five commonly reported quality parameters: dissolved oxygen, electrical conductivity, pH value, and total nitrogen and phosphorus concentrations. This paper explains the motivation and methodology of the EPI WATQI and demonstrates how hot-deck imputation of missing values can expand its geographical coverage and better inform decision-makers on the types and extents of water quality problems in the context of limited globally comparable water quality monitoring data.