Water Stress Index Calculator Formula

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

Use the Water Stress Index Calculator

Formulas Used

Water Stress Ratio

stress_ratio = withdrawals_km3 / renewable_supply_km3

Stress Percentage

stress_pct = withdrawals_km3 / renewable_supply_km3 * 100

Remaining Supply

remaining_km3 = renewable_supply_km3 - withdrawals_km3

Variables

VariableDescriptionDefault
withdrawals_km3Total Annual Withdrawals(km³/yr)30
renewable_supply_km3Renewable Water Supply(km³/yr)75

How It Works

Water Stress Index

The water stress index measures how much of a region's available water is being used. Higher ratios indicate greater pressure on water resources.

Formula

Water Stress = Total Withdrawals / Renewable Supply

Thresholds

  • < 0.10: Low stress
  • 0.10 - 0.20: Low-to-medium stress
  • 0.20 - 0.40: Medium-to-high stress
  • > 0.40: High stress (water scarcity)
  • > 0.80: Extremely high stress

    • Worked Example

    A region withdraws 30 km³/year from a renewable supply of 75 km³/year.

    withdrawals_km3 = 30renewable_supply_km3 = 75
    1. 01Stress ratio = 30 / 75 = 0.400
    2. 02Stress percentage = 40.0%
    3. 03Remaining supply = 75 - 30 = 45 km³/year
    4. 04At 40%, this region is at the high stress threshold

    Ready to run the numbers?

    Open Water Stress Index Calculator