National Water Security Index (NWSI)

Developed initially under the OECD Water Security Framework (2015) and later adapted by the European Commission, the NWSI has become the benchmark metric for prioritising investments, comparing results across countries, and tracking progress toward SDG 6.

Methodological structure

Availability: proportion of renewable water resources (m³/inhab.·year), national water balance, and interannual precipitation variability.‍

Quality: percentage of water bodies with “good status” according to the Water Framework Directive, and average concentration of nutrients and priority pollutants.‍

Risks: population and GDP exposure to droughts and floods (Return Period < 20 years) and coverage of parametric insurance.‍

Ecosystems: compliance with ecological flow requirements in main rivers and surface area of Ramsar wetlands in favourable condition.

Each sub-index is normalised on a 0–1 scale using historical percentiles (1990–2020) and weighted at 0.25. The final NWSI is the weighted arithmetic mean.

Interpretation

• NWSI ≥ 0.70 → High water security
• 0.50 – 0.69 → Moderate security (manageable gaps)
• < 0.50 → Low security (high water risk)

Global trends 2010–2024

• Northern Europe: average improvement of 0.05 points due to network digitalisation and river restoration.
• Mediterranean: 0.03-point decline due to persistent drought and rising temperatures (+1.4 °C).
• South Asia: average NWSI 0.41; rapid urbanisation and industrial pollution are major constraints.
• Latin America: stable trend (~0.59) but with strong heterogeneity between the Southern Cone and tropical regions.

Strategic applications of the NWSI

• EU funding allocation: the 2021–2027 Mechanism links 35% of water-related financing to NWSI progress.
• Country risk ranking: rating agencies (e.g., Standard & Poor’s) incorporate NWSI < 0.55 as a negative factor in sovereign debt assessments.
• Multilatina companies: use the NWSI to choose plant locations and prioritise resilience plans.

Improvement strategies: 2030 Roadmap

• Increase reuse of urban wastewater to 25% of total supply → expected improvement +0.03 points.
• Reduce network losses to 10% (Spain 2024: 19%) → +0.02 points.
• Ensure 80% of agricultural land is covered by parametric water-risk insurance → +0.01 points in the risk sub-index.
• Restore 15% of degraded wetlands and guarantee ecological flows in 100% of new permits → +0.02 points.

Integration with other indicators

• Water deficit and water vulnerability: provide the exposure dimension used in the risk sub-scale.
• AWARE: scarcity factor used to adjust the availability dimension at basin level.
• Corporate water neutrality: its replenishment KPIs enhance the local NWSI by increasing availability and resilience.

Limitations and upcoming developments

• Data consistency for water quality remains uneven in African regions; OECD plans to integrate Sentinel-2 remote sensing to close gaps.
• Urban-rural imbalance in risk weighting; differentiated weighting is proposed for the 2026 revision.
• Inclusion of virtual water imports indicator (IDH) to reflect external dependencies starting in 2027.

The NWSI condenses the complexity of water security into a single figure, becoming a compass for investments and public policy interventions. Countries with an NWSI < 0.60 must urgently mobilise capital for efficiency, digitalisation, and ecosystem restoration if they aim to avoid economic losses equivalent to 5% of GDP by 2030.