Reservoir Levels

Puerto Rico does not publish reservoir storage. The USGS parameter for reservoir volume returns no data for the territory, in real time or historically. What is published, every 15 minutes and with daily values going back decades, is the elevation of the water surface. So every figure on these pages is a level in metres above mean sea level. We do not convert it to a fill percentage, because the elevation-to-volume curve each dam would need is not public.

To answer "is this low?" without inventing a capacity, we compare today's level against every reading for the same calendar month across the whole record. A seasonal percentile of 8% means only 8% of that month's days on record were lower.

For the reservoirs it operates, the Puerto Rico Electric Power Authority publishes a six-step operating ladder: Overflow, Safety, Observation, Adjustments, Control and Out of service — published in Spanish as desborde, seguridad, observación, ajustes, control and fuera de servicio. That ladder is what actually triggers rationing on the island, so we show it as the official status. Two published ladders fail our consistency check and are shown without a status: Matrullas is published with thresholds identical to Garzas, a different dam some three metres higher, and Loco is published with its Control level below its Out of service level. We flag both rather than guess at the intended values.

Reservoirs operated by the Puerto Rico Aqueduct and Sewer Authority — including Carraízo, La Plata, Cidra, Toa Vaca, Río Blanco, Fajardo and Cerrillos — have no operating ladder published in an open format, so they carry level and seasonal standing only. Levels come from USGS; we cross-check them daily against PREPA's own operational feed, which agrees to the centimetre. Design capacities are from the US Army Corps of Engineers' National Inventory of Dams and describe dam size, not a fill divisor.