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Calcimator

Water Quality Index (WQI) Calculator

Calculate a composite Water Quality Index (0-100) from dissolved oxygen, pH, BOD, nitrate, phosphate, turbidity, and temperature change.

Inputs

% sat
mg/L
mg/L
mg/L
NTU
°F

Results

Water Quality Index

91.4 / 100

Classification

Excellent

Suitable UsesDrinking (with disinfection), recreation, aquatic life
DO Sub-Index88 / 100
pH Sub-Index98 / 100
BOD Sub-Index90 / 100
Nitrate Sub-Index90 / 100
Turbidity Sub-Index90 / 100
How to Use This Calculator
  1. Measure and enter Dissolved Oxygen (% saturation), pH, BOD5, Nitrate, and Phosphate from water samples.
  2. Enter Turbidity (NTU) and Temperature Change (degrees C above baseline).
  3. Review the Water Quality Index (WQI) — 91-100 is excellent, 71-90 good, 51-70 medium, below 51 is poor.
  4. Check Classification and Suitable Uses to communicate results to stakeholders.
  5. Use the sub-index scores (DO, pH, BOD) to identify the specific parameters driving water quality issues.

How the result changes with Dissolved Oxygen

Dissolved OxygenWater Quality IndexClassification
2079.9 / 100Good
7088.7 / 100Good
13088.7 / 100Good
18079.9 / 100Good

What each input means

Dissolved Oxygen
Dissolved oxygen as percent saturation. 100% = fully saturated at given temp/pressure. Below 60% stresses aquatic life.
pH
Water pH. Ideal range for aquatic life is 6.5-8.5. Values outside this harm most organisms.
BOD₅
5-day Biochemical Oxygen Demand. Measures organic pollution. Clean water: <2, polluted: >10 mg/L.
Nitrate
Nitrate concentration (NO₃-N). Drinking water limit is 10 mg/L. High levels cause eutrophication.
Phosphate
Total phosphate concentration. Levels >0.1 mg/L can trigger algal blooms in surface water.
Turbidity
Water clarity measured in Nephelometric Turbidity Units. Drinking water should be <1 NTU.
Temperature Change
Deviation from expected/natural temperature. Thermal pollution from industrial discharge is a common cause.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Dissolved Oxygen = 85, pH = 7.2, BOD₅ = 3, Nitrate = 5 = 7 input(s) provided
  2. Calculate Water Quality Index
    Water Quality Index
    91.4 = 91.4
  3. Calculate Classification
    Classification
    Excellent = Excellent
  4. Calculate Suitable Uses
    Suitable Uses
    Drinking (with disinfection), recreation, aquatic life = Drinking (with disinfection), recreation, aquatic life
  5. Calculate DO Sub-Index
    DO Sub-Index
    88 = 88

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