Water Stress Index Calculator Formula
Understand the math behind the water stress index calculator. Each variable explained with a worked example.
Formulas Used
Water Stress Ratio
stress_ratio = withdrawals_km3 / renewable_supply_km3Stress Percentage
stress_pct = withdrawals_km3 / renewable_supply_km3 * 100Remaining Supply
remaining_km3 = renewable_supply_km3 - withdrawals_km3Variables
| Variable | Description | Default |
|---|---|---|
withdrawals_km3 | Total Annual Withdrawals(km³/yr) | 30 |
renewable_supply_km3 | Renewable 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
Worked Example
A region withdraws 30 km³/year from a renewable supply of 75 km³/year.
- 01Stress ratio = 30 / 75 = 0.400
- 02Stress percentage = 40.0%
- 03Remaining supply = 75 - 30 = 45 km³/year
- 04At 40%, this region is at the high stress threshold
Frequently Asked Questions
What causes water stress?
Water stress results from growing demand (agriculture, industry, population) exceeding renewable supply, often worsened by drought, climate change, and poor management.
Which regions face the most water stress?
The Middle East, North Africa, South Asia, and parts of the American Southwest face the highest water stress. Over 2 billion people live in water-stressed regions.
Can water stress be reversed?
Yes, through efficiency improvements (drip irrigation, recycling), demand management, desalination, and watershed protection. Israel has reduced stress through aggressive water recycling.
Ready to run the numbers?
Open Water Stress Index Calculator