It is where liquid water evaporates into a gas and is carried in clouds or water droplets in the air. Later this gaseous water is rained onto the land back into a liquid.
H O + Heat <==> H O
(l)
2
(g)
2
It should be equal reverse and forward rates and does not favour a side. The water cycle is supposed to maintain water at roughly the constant level of liquid and gaseous states.
Since water is constantly being recycled, the water we drink today is the same water the dinosaurs used to bathe in.