the use of phase change materials (PCM). Two methods of introducing the PCM were considered: (1) encapsulated in the sidewalls and bottom of the pool, and (2) use the PCM in an external heat exchanger. Heat is stored when water temperature is sufficiently high, while it is released when water temperature drops below comfort levels. A numerical model was built and validated for predicting the evolution of the water temperature, by taking into account meteorological data at three different locations in north-east of Spain. The simulations showed that using phase change materials provided some improvement of water conditions, especially when used in an external heat exchanger.