Why to water (wet) bricks or concrete blocks before masonry wall construction?

As clay bricks inherently have high water absorption (to the tune of 20%), we should be ideally soaking bricks as they may absorb water present in cement mortar thus reducing the hydration of cement in mortar leading to reducing the mortar strength, adhesion and bonding with individual bricks/block.

You should avoid spraying of water on bricks or concrete blocks. It is always better to soak them in water (i.e., individually submerging and removing them till air bubbles ceases to come out) before initiating building a brick masonry wall.