Baseline Water Stress (BWS)

Baseline Water Stress (BWS) is an indicator that measures the ratio between total annual water withdrawals and the renewable water available in a given area. It is one of the headline indicators of the Aqueduct Water Risk Atlas developed by the World Resources Institute (WRI), and it expresses how much competition there is for water in a basin.

Definition and formula

In simple terms:

BWS = average annual withdrawals / long-term renewable water supply

WRI groups the result into stress categories. The widely used thresholds are:

• Below 10%: low stress.
• 10% to 20%: low to medium stress.
• 20% to 40%: medium to high stress.
• 40% to 80%: high stress.
• Above 80%: extremely high stress.

BWS takes account of agricultural, urban and industrial demand within the basin. Because it is based on long-term averages, it reflects structural pressure on water resources rather than a specific drought event.

How companies use it

• Screening suppliers and sites: identifying which facilities or suppliers sit in highly stressed basins so they can be prioritised for action.
• Setting water targets: reinforcing replenishment or efficiency commitments where stress is highest, in line with corporate water neutrality goals.
• Directing investment: prioritising nature-based solutions in catchments where they can ease pressure most effectively.

Strengths and limitations

• It is built on long-term averages, so it does not capture short, sharp drought episodes; it should be combined with drought and seasonal-variability indicators.
• It measures physical competition for water but not the quality of water governance, so it is best used alongside governance and regulatory indicators.
• It is a screening tool: a high BWS score flags a basin for closer study, not an automatic conclusion about a single operation.

BWS is often the first warning sign in supply-chain water risk and water risk assessment. Using it together with resilience and governance indicators gives a fuller picture of exposure. At Manglai we help companies measure their environmental footprint and prepare their sustainability reporting. Discover how Manglai can help you.