The water availability index (WAI) is a global measure of water available for socio-economic development and agricultural production. It represents the accessible water diverted from the runoff cycle in a give country, region or drainage basin, expressed as volume per person per year, m³/p/y. Critical values of the water stress index (WSI) identify various ranges of water scarcity. Present critical indexes are between 1700 m³/p/y (Postel) and 1000 m³/p/y (World Bank). These values are important because the World Bank and other international aid organizations use them to prioritize and to direct aid to developing nations. Two approaches to define water stress indices and scarcity are: Heuristic proportionality and empirical methods, and appropriations and calculations based on human and economic needs through food intake calculations and industrial use estimate. The critical ranges and definition of stress indexes are still actively discussed in the water resources community . To establish the validity and usefulness of these indices one needs to find a correlation with other indices that measure the degree of development or general economic well being of a country. The most likely indicator is the Gross Domestic Product (GDP.). Intuitively a positive correlation between GDP and WAI should exist, similarly to the well known per capita relation between energy consumption and GDP.

Recent data from the World Resources Institute (2002) were used to correlate WAI and development indicators and to plot global correlation diagrams of per capita WAI vs. GDP, vs. grain production, desalination and other factors. Surprisingly no correlation exists. Positive Correlation with GDP is achieved when plotted against total water consumption including the water equivalent of total grain imports (virtual water). Correlation is also enhanced when grouping the data set by hydrologic/climatologic categories into a regional classification of climate zones with variable stress (dry seasons) and chronic stress, and by excluding data above a threshold value about twice the critical Water Stress Index.

In order for the WSI to be an effective indicator for allocation of financial aid or technical assistance agro-economic and use efficiency factors have to be included in global factors now in use.7