Joy of movement
Joy of refreshing f/herse
Joy of lightness
Joy of having mom or dad very close
Joy of getting attention
Water
In the soft wet element, at almost zero gravity, babies can easily move around and explore new possiblities they wouldn't be able to experience outside of the water. Babies get a lot of impulses when water touches their skin.
Trust
Building trust in water, in live, in parents and in himself/herself.