First, since it's a sunny day, this water will turn into steam and evaporate into the atmosphere. This is where condensation takes place, and the steam forms into clouds. After a lot of water build-up in these clouds, precipitation takes place, meaning the clouds rain all the water they've gained. All this water collects, and the cycle begins once again.
The pool of water is exposed to sunlight (as the day is sunny) that means that all the water in the pool will heat to the point of evaporation into water vapor. In this case, the water goes from the liquid state to the gaseous state where it will be captured by the clouds. This process happens to all bodies of water on the planet (rivers, oceans and etc.). The clouds capture so much water vapor that they are overloaded to the point where they discharge all the water vapor into liquid water through precipitation.
