If the first part of nephron action is called filtration what is the second part of the process called, where the precious water is returned back into the blood?

Reabsorption

Explanation:

The kidney is the organ where filtration of the blood and other bodily fluids takes place. The process of filtration involves the separation of the soluble and useable components like water and waste from the blood into the glomerulus.

Reabsorption can be define as the absorption of ions, molecules and water obtain as a result of filtration process back into the bloodstream to maintain the homeostasis.