4.2.9 (HL)—Freshwater planetary boundary

The freshwater boundary asks whether human changes to water flows and stores threaten a safe operating space for people and ecosystems.

Measure pressure with indicators such as withdrawal relative to recharge and environmental-flow needs, distinguishing river, groundwater and root-zone water by basin and season. Mitigation can combine efficiency and reuse, abstraction limits, protected environmental flows, aquifer recharge and restoration of wetlands or catchments.

A national average may look safe while one river is over-abstracted and its environmental flow fails in summer.

Water risk is spatial and seasonal; safe levels depend on local flows, ecosystems and recharge.

A boundary indicator is not a household allocation or an exact universal tipping line.