Semi-annual Index · H1 2026
Reservoir Transparency Index
How openly and accessibly do countries publish their national reservoir storage data? We grade 167 countries across 7 dimensions — from raw data availability to API quality, historical depth and usability — and set aside 27 with no significant reservoirs.
Countries rated
167
+ 27 not rated (N/A)
Global average
33.8
Top score
89
Norway
Dimensions
7
World map
Reservoir Transparency by Country
Click any country to view its full evaluation. Countries in dark gray are not rated — they have no significant reservoirs (atolls, microstates, desalination economies) and are listed separately below.
Leaders
Needs Improvement
Norway
Excellent
Yemen
Opaque
Netherlands
Excellent
Somalia
Opaque
Australia
Excellent
Sudan
Opaque
Full rankings
All 167 Rated Countries · 2026
Click any country to view detailed scores and justifications. Dimension columns are shown on desktop.
Not rated
27 Countries with No Significant Reservoirs
These countries are set aside rather than graded. Having no significant reservoir storage is a geographic fact — atolls, microstates, desert and desalination economies — not a transparency failure, so giving them an “F” would be misleading. Each is listed with the reason and where it actually gets its water.
Show 27 not-rated countries
- BahamasN/A
No surface reservoirs: flat limestone islands where rivers are ephemeral.
Water supply: Freshwater groundwater lenses on the outer islands plus reverse-osmosis desalination (~90% on New Providence).
- BahrainN/A
A desert island with negligible rainfall, no rivers and no catchments; reservoirs cannot exist.
Water supply: 100% desalination operated by the Electricity and Water Authority (EWA).
- BarbadosN/A
No surface reservoirs: coralline-limestone karst, all rivers ephemeral.
Water supply: Over 90% from groundwater wells (limestone aquifer), the remainder from desalination.
- Cape VerdeN/A
No reservoirs above the qualifying scale: only micro-dams (Poilao ~1.7 hm³, Faveta, Saquinho).
Water supply: Reverse-osmosis desalination and groundwater, with minor agricultural dams.
- ComorosN/A
No surface water on the main island (Grande Comore) and no impoundments.
Water supply: Rainwater harvesting and marginally fresh coastal groundwater.
- DjiboutiN/A
Arid, with no perennial rivers or surface reservoirs.
Water supply: Groundwater boreholes plus the Doraleh desalination plant (since 2021).
- GambiaN/A
No significant surface reservoirs: the Gambia River is undammed.
Water supply: Almost entirely shallow groundwater (NAWEC).
- Guinea-BissauN/A
No large operational dams (the Corubal/Saltinho and Geba projects remain unbuilt).
Water supply: Groundwater supplied via EAGB.
- KiribatiN/A
No surface reservoirs: coral atolls with no rivers.
Water supply: Freshwater lenses (Bonriki and Buota) piped by the Public Utilities Board, plus rainwater harvesting.
- KuwaitN/A
Desert with no rivers or surface reservoirs.
Water supply: ~92% coastal desalination plus strategic distribution storage tanks.
- LiechtensteinN/A
An Alpine microstate in the Rhine valley with no storage reservoirs.
Water supply: Spring and groundwater sources via Liechtensteinische Kraftwerke (LKW).
- MaldivesN/A
No surface reservoirs: low coral atolls with no rivers; only distribution storage tanks exist.
Water supply: Reverse-osmosis desalination (Male) plus rainwater harvesting.
- MaltaN/A
A riverless limestone archipelago with no surface reservoirs.
Water supply: ~64% reverse-osmosis desalination and ~36% groundwater boreholes.
- Marshall IslandsN/A
No hydrological reservoirs: coral atolls (max ~2 m elevation); the Majuro airport-catchment tanks are distribution storage, not impoundments.
Water supply: Airport rainwater catchment, reverse-osmosis desalination and shallow groundwater lenses.
- Micronesia (Federated States)N/A
No significant reservoirs: small Pacific islands without managed impoundments.
Water supply: Rainwater catchments, shallow groundwater wells and limited piped systems.
- MonacoN/A
A 2 km² city-state with no rivers or impoundments.
Water supply: Six local underground springs stored in distribution cisterns, plus water purchased from France (Var and Vesubie).
- NauruN/A
No reservoirs: a 21 km² raised-phosphate island with no rivers or impoundable terrain.
Water supply: Five reverse-osmosis desalination units (Nauru Utilities Corporation) plus rooftop rainwater.
- QatarN/A
Flat desert with no rivers and no reservoirs above the qualifying scale.
Water supply: 100% seawater desalination (Kahramaa); only strategic distribution tanks exist.
- Saint Kitts and NevisN/A
No storage reservoirs above the qualifying scale: surface intakes feed only small distribution tanks (20,000-1,000,000 gal).
Water supply: ~30% river surface intake and ~70% groundwater wells; a Basseterre desalination plant was commissioned in 2026.
- San MarinoN/A
A landlocked microstate with no significant rivers or reservoirs.
Water supply: Supplied through the Italian water network (state utility AASS).
- São Tomé and PríncipeN/A
No reservoirs above the qualifying scale: only minor run-of-river hydropower (Contador).
Water supply: River intakes and springs (EMAE); impoundment is negligible.
- Solomon IslandsN/A
No operational water-supply or hydropower storage reservoirs (Tina River is run-of-river; Gold Ridge is a mine tailings dam).
Water supply: Rivers and groundwater on Guadalcanal (Solomon Water).
- Timor-LesteN/A
No significant storage reservoirs (Belulik Leten is a small irrigation dam).
Water supply: River intakes and groundwater (EDTL and local systems).
- TongaN/A
No surface reservoirs: relies on a groundwater lens, with no rivers.
Water supply: Groundwater wellfields beneath Tongatapu managed by the Tonga Water Board.
- TuvaluN/A
No surface reservoirs: nine low-lying atolls with no rivers or terrain capable of impoundment.
Water supply: Rainwater harvesting into household and community tanks plus solar-powered reverse-osmosis desalination.
- VanuatuN/A
Only small run-of-river hydropower with negligible impoundment.
Water supply: Groundwater and stream intakes (UNELCO / VUI).
- Vatican CityN/A
A 0.44 km² city-state with no rivers, catchments or reservoirs.
Water supply: Supplied entirely through the Italian municipal and aqueduct network.
Methodology
How the RTI is calculated
Each country is scored on 7 dimensions with different weights reflecting their importance to practical data usability. Coverage carries the highest weight (30%), followed by Data Availability (20%). All evaluations are based on primary evidence and are publicly auditable.
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Open data
Download the dataset
The full RTI dataset — all country scores, dimension breakdowns and metadata — is freely available as JSON, CSV and PDF. No registration required.