Water quality index is a 100-point scale that summarizes results from a total of nine different measurements when complete.
Using the book Field Manual for Water Quality Monitoring, the National Sanitation Foundation surveyed 142 people representing a wide range of positions at the local, state, and national level about 35 water quality tests for possible inclusion in an index. Nine factors were chosen and some were judged more important than others, so a weighted mean is used to combine the values.
So that field measurements could be converted to index values, respondents were asked by questionnaire to graph the level of water quality (0 through 100) corresponding to the field measurements (e.g., pH 2-12). The curves were then averaged and are thought to represent the best professional judgment. The updated calculator allows you to enter the latitude and longitude for the site or pick this location from the Google Earth Map. The calculator completes the individual and group calculation and permits you to generate a customized report.