Yes, the water in Siam Park (located in Tenerife, Spain) is heated to approximately 25°C (77°F) throughout the year. This makes the park, often cited as the best water park in the world, a viable destination even during the cooler winter months in the Canary Islands. The park actually markets itself as the "first air-conditioned outdoor aquatic park in the world" because of this temperature control. While 25°C is comfortable for active sliding, some visitors may find the water feels slightly "brisk" when first stepping in if the ambient air temperature is lower, but it is certainly warm enough for all-day enjoyment. Additionally, Siam Park utilizes an advanced eco-friendly system where the water used in the slides is desalinated on-site and later recycled to water the park's vast array of tropical plants and vegetation, maintaining its status as a "green" water park.