I heard the fact that what water dinosaurs drank and excrete and drink that water only that means we are recycling water but how the molecules of water clear and how it become safe for drinking ?

Dear student
Its actually the water cycle. When the liquid gets so heavy it can’t stay in the atmosphere anymore, it falls, or “precipitates,” as rain, snow. Once the precipitation reaches the ground or lands in lakes, oceans, and rivers, the cycle continues. So water molecules stays same and is safe for drinking. 
Regards