Hydrology
1. The science encompassing the behavior of water as it occurs in the           
 atmosphere, on the surface of the ground, and underground. 

2. The science thatrelates to the water of the earth. 

3. The science treating  of the waters of the earth, their occurrence, 
    distribution, and movements.            

4. In practice the study of the water of the oceans and the atmosphere
    is considered part  of the sciences of oceanography and meteorology.