Together with co-authors Alexander de Sherbinin (Columbia University), Genevieve Carr (Northern Oil and Gas Branch, Indian and Northern Affairs Canada) and Carrie Rickwood (Natural Resources Canada) Tanja Srebotnjak, Senior Fellow at Ecologic Institute, published a study in the journal Ecological Indicators on the design and testing of a global water quality index.

The so-called WATQI had originally been developed for the Environmental Performance Index and further improved in this study using a more robust method to fill persistent gaps in global water quality data. The index combines five parameters, including pH value, dissolved oxygen, total phosphorus and nitrogen concentrations as well as electrical conductivity, to assign a value between 0 (worst) and 100 (best) to 142 countries. The imputation method used to fill data gaps was shown to result in estimates that did not substantially alter the distributional characteristics of the observed values and does not produce unrealistic or extreme values as other methods can.

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 & 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 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.