This calculator requires the use of Javascript enabled and capable browsers. This script creates a method of calculating the water quality index of a test body of water using only the temperature of the nine normal factor conditions usually tested. The logical process is to subtract the last previous temperature from the current temperature and record the result as temperature change in degrees Celsius (C). Enter that value and click on Calculate to determine the water quality index. The default of no temperature change yields a WQI of 93.