The water that fills the canal is from several rivers that were dammed to create Lago Gatún (Lake Gatún).
The rainy season helps to replenish Lago Gatún–from which Panama City also gets its drinking water–and other freshwater reserves for the country. Besides providing drinking water and feeding the Panama Canal, these rivers also help people by providing sources of alternative energy. Just like in Tennessee, where TVA has built many dams to provide hydroelectric power, some dams provide energy in Panama. Almost 70% of Panama’s electricity comes from hydroelectric power, whereas in TN, that number is around 15%. Panama still relies heavily on oil and coal, though, with around 35% of its total energy use coming from renewables (about half of that being hydropower).
In recent years, climate change has made the rainy and dry seasons more unpredictable. This past year, the rainy season didn’t pick up until around July, but even then, the rains were short and infrequent. This past year was also an El Niño year, which is a cyclical pattern of air and water temperatures that decreases rainfall. The ongoing drought, made worse by El Niño, led to extremely low water levels in the Panama Canal, which made it difficult for ships to pass through, costing Panama a lot of money–around $100 million every month.
Remember also that Lago Gatún provides the capital city, and about half of all of Panama’s residents, with drinking water. Each passage of a boat through the Panama Canal uses about 52 million gallons of water.
