Water Quality Index Calculator Formula

Understand the math behind the water quality index calculator. Each variable explained with a worked example.

Use the Water Quality Index Calculator

Formulas Used

Water Quality Index

wqi = weighted_sum

DO Contribution

rating = do_score * 0.30

Turbidity Contribution

turbidity_contrib = turbidity_score * 0.20

Nutrient Contribution

nutrient_contrib = nutrient_score * 0.20

Variables

VariableDescriptionDefault
do_scoreDissolved Oxygen Score(0-100)75
ph_scorepH Score(0-100)80
turbidity_scoreTurbidity Score(0-100)70
temp_scoreTemperature Score(0-100)85
nutrient_scoreNutrient Score(0-100)65
weighted_sumDerived value= do_score * 0.30 + ph_score * 0.15 + turbidity_score * 0.20 + temp_score * 0.15 + nutrient_score * 0.20calculated

How It Works

How to Calculate Water Quality Index

The WQI combines multiple water quality parameters into a single score.

Formula

WQI = DO(0.30) + pH(0.15) + Turbidity(0.20) + Temp(0.15) + Nutrients(0.20)

Rating Scale

  • 90-100: Excellent
  • 70-89: Good
  • 50-69: Medium
  • 25-49: Bad
  • 0-24: Very Bad

    • Each parameter is first converted to a 0-100 sub-index score based on its measured value.

    Worked Example

    A water body with DO=75, pH=80, Turbidity=70, Temperature=85, Nutrients=65.

    do_score = 75ph_score = 80turbidity_score = 70temp_score = 85nutrient_score = 65
    1. 01DO: 75 * 0.30 = 22.5
    2. 02pH: 80 * 0.15 = 12.0
    3. 03Turbidity: 70 * 0.20 = 14.0
    4. 04Temperature: 85 * 0.15 = 12.75
    5. 05Nutrients: 65 * 0.20 = 13.0
    6. 06WQI = 22.5 + 12.0 + 14.0 + 12.75 + 13.0 = 74.3 (Good)

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