Story and history
The yatra retells a legend, as devotees tell it. When the gods and asuras churned the Ocean of Milk, poison rose before the nectar; Shiva drank it to save the world and began to suffer from its heat, until his devotee Ravana carried Ganga water in a kanwar to the temple at Pura Mahadev and poured it over him. Every Shravan the pilgrims repeat that journey.
As a historical practice, the earliest mention identified by Professor Devi Prasad Dubey of the University of Allahabad goes back to the 1700s, when pilgrims carried water from Sultanganj to the Vaidyanath shrine at Deoghar. That route, about 105 km on foot, is still walked in Shravan by the Bol Bam pilgrims. After the 1960s the custom spread to the towns, and it grew sharply in the 1980s, with better roads.

