After the test is completed and the results are recorded, the Water Quality Index (WQI) for the body of water can be computed. To formulate a WQI, you must first compute a Q- value for the results you obtained. The Q-values of all nine tests will be used together to determine the health of the river or lake. See Water Quality Index page. To compute the Q-value for the dissolved oxygen test, follow these steps:

1. Find the weighting curve chart at the end of this page;
2. Locate your test result on the bottom (horizontal or “x” axis) of the char;
3. Interpolate the Q-value for your test result using the following steps;
1. From your test result value on the horizontal (“x”) axis of the chart, draw a vertical line up until it intersects the weighting curve line;
2. From this point of intersection, draw a horizontal line to the left hand side (the vertical or “y” axis) of the chart.
3. Where this horizontal line intersects the vertical (“y”) axis of the chart, read off the value. This is the Q-value for this test; it should be recorded in Column B on the WQI chart on the Water Quality Index page.

The Q-value for each test should then be multiplied by the weighting factor listed in the chart on the Water Quality Index page. Record the product of this calculation in Column D of the chart.

Nitrate: mg/L Note: If NO-3>100.0, Q=1.0