Only 11% of the world’s transboundary country-aquifer pairs have any cooperation agreement at all

Of 568 pairings between a country and an aquifer it shares with a neighbor, only 11% have any operational cooperation arrangement in place, and fewer than 5% are covered by a formal treaty. The count comes from researchers at United Nations University’s water institute, UNU-INWEH, who mapped 426 known transboundary aquifers that run beneath nearly every international land border. Together those aquifers sit under about 35% of the world’s groundwater-irrigated cropland.

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In plain numbers, 11% of 568 works out to roughly 62 pairs with a working arrangement, and fewer than 5% to fewer than 28 with a treaty. The remaining pairs, several hundred of them, have neither. Because that cropland feeds a large share of irrigated agriculture, the gap is a food-supply question as much as a water-law one.

Counting pairs, not aquifers

The unit of the analysis matters, because one aquifer can be shared by several countries and each country’s stake counts separately. The 568 “country-aquifer pairs” in the release on the study are therefore more numerous than the 426 aquifers themselves. Within that set, 11% report an operational cooperative arrangement, and a formal treaty is rarer still, covering fewer than 5% of pairs.

Put simply, in roughly nine of every ten cases, a country draws on groundwater that crosses its border without any operational arrangement with its neighbor over how that water is used. Even in the pairs that do cooperate, the release does not say how strong or enforceable the arrangement is, only that one is reported. The finding comes from a policy brief that UNU-INWEH published on October 19, backed by an analysis listed as in press at the Proceedings of the National Academy of Sciences.

Same average depletion, different geography

The study’s second finding is less intuitive. On average, depletion in shared aquifers is no greater than in comparable aquifers that lie wholly inside one country. What differs is geography. Inside shared aquifers, groundwater-dependent irrigation and depletion cluster closer to the international border, a pattern the authors did not see in domestic aquifers.

The authors sorted the pairs by how close irrigated farming sits to the line. In 71% of pairs there is limited groundwater-dependent farming near the border. In 22% it is spread across the border region, and in 7% it is highly concentrated at the boundary itself.

Dr. Marc F. Müller, the UNU-INWEH associate research professor who led the brief, put the point this way: “Countries often treat a shared aquifer as one shared problem, but that is rarely how groundwater behaves.”

The authors are careful about what the proximity shows. Border-hugging pumping does not prove that one country is lowering its neighbor’s water table or cutting well yields. It flags where a local hydrogeological assessment is needed, because only that work can show whether pumping effects cross the line.

That is why the brief’s first recommendation is mapping rather than negotiating. Countries are urged to chart groundwater demand and depletion relative to the border, alongside the hydrogeology that decides whether pumping effects can cross it. A government that knows its heaviest irrigation sits fifty kilometers inland faces a different problem from one whose wells ring the boundary, and the study argues the two should not be handed the same template agreement.

Setbacks in the desert, shared pumping in Geneva

The brief offers two models for how cooperation can work, depending on where the wells are. Where intensive use is away from the border, it recommends monitoring, data sharing and zone-based measures such as pumping setbacks or protected areas. Its example is the arrangement between Jordan and Saudi Arabia over the Al-Sag/Al-Disi aquifer, which includes protected areas.

Where use is concentrated along the border, the brief calls for coordinated pumping volumes and, where relevant, joint management of recharge. The example there is the long-standing approach France and Switzerland take to the Genevois aquifer.

UNU-INWEH Director Kaveh Madani, a co-author, framed the urgency in the institute’s statement: “In an era of global water bankruptcy, shared groundwater is too valuable to manage on assumptions.” The authors also urge action before new wells and fields move toward borders, since that keeps more options open. They link the timing to preparations for the UN 2026 Water Conference in December. The institute’s press release sets out the same recommendations, and Smart Water Magazine reported on the finding that depletion and irrigation concentrate near borders.

The policy brief also runs an illustrative irrigation scenario, which its authors stress is not a prediction. Under it, the number of “Border Locked” pairs, where farming concentrates at the boundary, rises from 40 to 87, and “Distributed Agriculture” pairs rise from 125 to 211. Whether governments will begin negotiating before those fields are dug is the open question the December conference now faces.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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