The Water Quality Index (WQI) is useful to indicate the general health of a water body based on up to nine water quality parameters. The form looks like this:
Most parameters allow you to select only one matching PCode, however some (Phosphate, Nitrates, and Solids) often are estimated by adding two lab or field measurements, so you can select up to two PCode for these. If you already have total values for these parameters in your source table, just select that one in the first of the two drop-down boxes and leave the second one at (Not Used). Finally, the WQI method requires the difference between the site water temperature and a coincident reference site temperature. If used, you will need to have the reference site temperatures available but be assigned the same station ID as the test site yet have a different PCode. Alternatively, select (Set Temperature Change to Zero) and a zero delta temperature will be used in the WQI calculation.
The WQI calculator has subindex relationships programmed in for each of the nine variables, and the weighted average WQI is based on standard weights for each variable. For those instances in which a PCode is not selected or data are not found, that subindex is not included in the weighted average of the WQI (that is, the subindex is not set to zero, it is just ignored in the WQI calculation).
For more information, see http://www.water-research.net/watrqualindex/waterqualityindex.htm.