Why do our hands feel cold when wet?

Because the water on our hands evaporates, and thus heat is taken from them.

Why is the air cooler after a rain?

Because evaporation then takes place from every wet object, and this absorbs heat from the air.

Why does watering streets and roads cool the air?

Because the water evaporates and absorbs heat from the air, making it cooler.

Why do we feel cold when our clothes are wet?

Because the moisture in them evaporates and absorbs heat from our bodies.

Why is wet land always cold?

Because so much heat is absorbed from the land in the evaporation which is constantly taking place.