Water Stress Index (WSI)

The Water Stress Index (WSI) is a key tool used to measure the relationship between the water available in a region and the demand generated by human activities. It has become a reference indicator in environmental studies and corporate strategy, as it helps identify critical areas, plan resource allocation and assess risks associated with water scarcity.

In a context of growing pressure on water resources, driven by climate change, population growth and agricultural and industrial intensification, the WSI carries strategic importance for the food, energy and economic security of countries.

Evolution of the concept

The WSI emerged in the 1980s as an academic indicator, and its use has since expanded across several types of organisation:

• International institutions such as the FAO and the European Environment Agency.
• Corporate assessment tools such as WWF's Water Risk Filter and the World Resources Institute's Aqueduct platform.
• Sustainability standards such as ISO 14046, which incorporates a water stress characterisation factor.

Variables considered

WSI calculations can include several variables:

• Natural water availability: river flows, aquifer recharge and reservoir storage.
• Human demand: agricultural, industrial and urban water use.
• Environmental water requirements needed to sustain ecosystems.
• Climatic variability: droughts and extreme precipitation events.
• Water management and efficiency: losses in distribution networks and storage infrastructure.

Applications of the Water Stress Index

1. Public policy and water governance: assess the hydrological sustainability of a territory, prioritise investment in water infrastructure, and develop drought plans and climate adaptation policies.
2. Corporate sustainability and business strategy: identify supply-chain water risks, select safe locations for new facilities, and report through frameworks such as GRI and CDP Water Disclosure.
3. Science and research: environmental impact assessments and modelling of climate change effects on water resources.

Regulation and reference frameworks

• ISO 14046:2014, water footprint: incorporates water stress as a characterisation factor.
• EU Water Framework Directive (2000/60/EC): requires maintaining the good status of water bodies.

Criticisms and limitations

• Over-simplification: the index does not always reflect water quality or efficiency of use.
• Scale issues: results vary depending on whether the index is calculated at basin, regional or national level.
• Lack of reliable data in many developing countries.

The Water Stress Index is a strategic tool for anticipating risks, shaping policy and guiding corporate sustainability in a world where water is increasingly scarce. Strengthening its use in hydrological planning, agricultural management and corporate decision-making helps ensure that water availability does not become an insurmountable constraint on development. At Manglai we help companies assess their water and carbon footprints and prepare their sustainability reporting. Discover how Manglai can help you.