Nirjala Ekadashi takes its name from the rule that governs it: nirjala, "without water." The fast is total, from sunrise on the eleventh day until the parana the next morning, with no food and no drink. Tradition holds that a person who cannot keep every Ekadashi through the year may keep this one and gain the benefit of all of them. It is common to give away water pots, fans, fruit and umbrellas on this day, since it falls in the hottest part of the North Indian summer.
The fast is on the eleventh tithi of the waxing fortnight of Jyeshtha, the period just before the monsoon. As with every Ekadashi, the parana is done in a window after the tithi ends, and its timing depends on the city's sunrise.
The observance is linked in the Mahabharata to Bhima, and for that reason it is also called Bhimseni or Pandava Ekadashi, especially in Gujarat and the west.