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Water Quality Index Calculator

Q: What is the Water Quality Index (WQI)?

WQI is a single composite score (0–100) aggregating multiple physical, chemical, and biological water quality parameters.

Q: What parameters are commonly used in WQI calculation?

Dissolved Oxygen (DO), pH, BOD5, Temperature change, Total Phosphate, Nitrates, Turbidity, and Total Dissolved Solids.

Q: What WQI score range indicates excellent water quality?

A WQI score of 90–100 represents Excellent water quality; 70–89 is Good; 50–69 is Medium; below 50 is Poor.

Calculate the Water Quality Index (WQI) based on key parameters including pH, dissolved oxygen, turbidity, and total dissolved solids.

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Calculation Parameters

Specify your stoichiometry inputs.

pH Level

4.010.0

Dissolved Oxygen (DO, % Saturation)

0%140%

Turbidity (NTU)

0 NTU100 NTU

Total Dissolved Solids (TDS, mg/L)

0 mg/L1,000 mg/L

Calculated Result

Water Quality Index (WQI) 91.2

Quality Rating Excellent

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Expert Tip

A WQI score above 90 indicates excellent water quality, while values below 25 indicate very bad quality water.

How this Calculator Works

This calculator evaluates the overall Water Quality Index using parameters like pH, dissolved oxygen, turbidity, and total dissolved solids. Adjust parameters below:

pH Level: Acidity or alkalinity measure (Ideal is ~7.0)
Dissolved Oxygen (DO): Amount of oxygen gas dissolved in water (Ideal is 100%)
Turbidity: Measurement of water clarity in NTU (Ideal is close to 0)
Total Dissolved Solids (TDS): Combined inorganic salts and organic matter (Ideal is <100 mg/L)

The results are computed instantly and updated in the results panel on the right.

Formula & Methodology

WQI = 0.20 * q_pH + 0.30 * q_DO + 0.25 * q_Turb + 0.25 * q_TDS where q represents sub-index percentage ratings from ideal values.

Where:

q_pH: Sub-index rating for pH.
q_DO: Sub-index rating for Dissolved Oxygen.
q_Turb: Sub-index rating for Turbidity.
q_TDS: Sub-index rating for TDS.

Step-by-Step Calculation Example

To compute the WQI manually using the default inputs, follow these steps:

Identify the input parameters. For example:
- pH = 7.2, DO = 90%, Turbidity = 4 NTU, TDS = 150 mg/L
Apply the formula:
1. Calculate pH rating: q_pH = 100 - 15 * |7.0 - 7.2| = 97.0 2. Calculate DO rating: q_DO = 90.0 3. Calculate Turbidity rating: q_Turb = 100 - (4 * 1.5) = 94.0 4. Calculate TDS rating: q_TDS = 100 - (150 * 0.1) = 85.0 5. Combine weights: WQI = (97 * 0.2) + (90 * 0.3) + (94 * 0.25) + (85 * 0.25) = 91.15 (Excellent)
Verify the calculated value which is updated instantly in the results panel on the right.