Water availability index based on quality and quantity: Its application in Mexico

This paper presents an Availability Index based on water quality and quantity. The Index has two elements, the first one indicates the water availability in terms of quantity (renewable freshwater), and the second indicates the quality (in terms of the treatment needed to obtain adequate quality for a potential use). Water quality is based on the calculation of another index called Potential Use Index, which enables one to classify the water in terms of its measured quality and to determine its suitability for a defined use. This methodology was applied to Mexico and it allowed a new regionalisation of the country for establishing several water quality preservation programs to start. Also, results were employed to redefine the national monitoring system as well as to initiate a process to change the water quality standards of Mexico. The Availability Index has the advantage of being very simple to evaluate and suitable for countries with no systematic monitoring (same type of information for different regions, regular periods of sampling and historical records).