The Brahma Vaivarta Purana narrates the story behind the Nirjala Ekadashi vrata vow.

Bhima, a lover of food, wanted to observe all ekadashi fasts, but could not control his hunger.

[5] The water-less fast is considered extremely difficult to follow as the day falls in the hot Indian summer and thus, it is deemed as very pious austerity.

[2][6] The devotee is however permitted to have a single tiny drop of water as part of the Achamana purification ritual.

Devotees remain awake the whole night and sing praises of Vishnu or meditate on his image.

[6] One who completes the vrata of Nirjala Ekadashi is mentioned to gain the favour of Vishnu, who grants him happiness, prosperity and forgiveness for sins.

Yama then judges the person's deeds and sends him to Svarga (heaven) or Naraka (Hell).