The Poor Man's Friend is the god of material prosperity in general, and the god of the rain in particular.

You will secure material prosperity, or both, by worshiping him.

He is Shiva, under a new alias, and he abides in the bottom of that cistern, in the form of a stone lingam.

You pour Ganges water over him, and in return for this homage you get the promised benefits.

If there is any delay about the rain, you must pour water in until the cistern is full; the rain will then be sure to come.
4.Fever.