Every country on earth that operates a reservoir knows, to the cubic metre, how much water it is storing right now. Almost none of them will let you see it.
That single gap is what the Reservoir Transparency Index (RTI) sets out to measure. This is the H1 2026 edition — the inaugural release of what will be a semi-annual index, re-graded every half-year. The first results are, frankly, worse than we expected.
Why a semi-annual index
Transparency is not a fixed property of a country. Data feeds open and close. In May 2025, Kyrgyzstan abruptly pulled its flagship reservoir's storage data offline; a country that publishes openly today can go dark next quarter, and a closed one can open up after a reform or a new portal launch.
An index published once a year would lag those changes by up to twelve months. So the RTI runs on a half-yearly cadence: this is H1 2026 (the first half of the year), and the next re-grade — H2 2026 — will pick up every feed that has opened or closed in between. The goal is a steady, predictable drumbeat of accountability rather than a once-a-year verdict that is half out of date by the time it lands.
What the RTI actually measures
The RTI does not score how much water a country has, how well it manages drought, or how impressive its dams are. It scores one thing: can the public see the data?
For H1 2026 we evaluated 194 countries against seven dimensions, each weighted by how much it bounds the usefulness of the rest:
- Coverage (30%) — what share of the country's total reservoir storage capacity has public data. This is the gatekeeper dimension, and it is capacity-weighted: a country that publishes its three biggest dams but hides two hundred small ones can still score well, because those three may hold most of the water.
- Data Availability (20%) — completeness and granularity of what is published.
- Technical Accessibility (15%) — APIs, downloadable formats, open licensing.
- Historical Depth (12.5%) — how many years of series you can actually reach.
- Update Frequency (10%) — how fresh the published numbers are.
- Methodological Transparency (7.5%) — whether measurement methods and capacity figures are documented.
- Language and Usability (5%) — whether a motivated outsider can navigate the portals.
Coverage carries the most weight on purpose. A country with a beautiful real-time API for 4% of its storage is less transparent than one with a clunky weekly PDF covering 90% of it. Everything downstream of coverage — accuracy, history, frequency — only matters for the reservoirs you can actually see. The full breakdown lives in the methodology.
The headline: most countries fail
Of the 194 countries, 167 were graded and 27 were marked structurally not-applicable — desert states and coral islands with no reservoirs to report, which we deliberately refuse to score as zero (more on that decision in a separate post).
Among the 167 graded countries:
- Only 5 earned an A.
- 92 — more than half — scored an F.
- The median country in the world scores F on public reservoir transparency.
This is the finding that justifies the whole project. Reservoir data is not a niche openness problem at the margins; opacity is the global default. Roughly one country in three publishes something genuinely usable. The rest range from token PDFs to total silence.
The leaders
The top of the table is dominated by small, water-aware, high-trust states — not by the countries with the most water or the biggest dams.
| Rank | Country | Score | Grade |
|---|---|---|---|
| 1 | Norway | 89.3 | A |
| 2 | Netherlands | 87.9 | A |
| 3 | Australia | 86.7 | A |
| 4 | Taiwan | 86.6 | A |
| 5 | Israel | 86.2 | A |
Norway tops the index not because it has the deepest data infrastructure on earth — the United States arguably does — but because it mandates publication of essentially all its reservoirs and ships them in a clean, open, machine-readable feed. Coverage beats depth.
Two results further down are worth flagging now because they capture the whole thesis:
- Cyprus ranks 7th (82.3, A−) — a country of 1.2 million people, with no public API, outranking most of the G20. Water-scarce nations build better data infrastructure because scarcity forces the issue.
- The United States ranks 8th (81.4, A−). The country with the single richest reservoir-monitoring apparatus on the planet is kept out of the top five by fragmentation: world-class data, scattered across agencies, with no single open front door.
The opposite end
At the bottom, the F-grade band is not empty space — it is full of countries that have the data and choose not to share it. Egypt operates 24/7 monitoring of Lake Nasser, one of the largest reservoirs on earth, and publishes none of it. Ethiopia inaugurated Africa's largest dam in 2025 and discloses nothing about how full it is. Kyrgyzstan published its flagship reservoir's storage for years, then abruptly pulled it offline in May 2025.
These are not capacity failures. They are choices. We unpack the pattern — and why it clusters along contested rivers — in Strategic withholding.
Why we built this
Reservoir levels decide whether farms get irrigated, whether cities ration, and whether downstream neighbours go to war over a river. When that data is hidden, the people most affected are the ones kept in the dark. A transparency index does not open the data by itself — but it makes the gap legible, comparable, and embarrassing, and that is where pressure starts.
The RTI is a living, semi-annual index. The methodology, scores and country-by-country evidence behind H1 2026 are all public at reservoirs.earth/transparency-index. If you find an error — a portal we missed, a feed we marked closed that is actually open — tell us before the H2 2026 re-grade. Getting it wrong in public, and fixing it in public, is the entire point.