The chemical report water quality rating consists of a numeric score from 0 to 100 and a descriptive score of excellent, good, fair and poor. Values must be entered for all parameters (except that you can enter either a value for turbidity or a value for transparency) to get a score.
The ratings are based on the water quality manual developed by Mitchell and Stapp in 1986. Raw values for each parameter and converted into Q--values and then are weighted based on the parameter's importance to overall water quality. The Q-values are multiplied by the weighting factors. The results for all of the parameters are added together to produce a score of 0-100. These scores are translated into descriptive scores as follows:
Excellent = 71-100
Good = 51-70
Fair = 31-50
Poor = 0-30