Here is your short paragraph on Nirjala Ekadashi:
It occurs on the eleventh day of the bright fortnight in the month of Jyeshta (July). Devout Hindus do not take even a drop of water on this day and this is why it is called ‘Nirjala’ (means without water).
Legend has it that Bhima, the second son of the Pandava brothers once asked Vyas to advise him of any single day when he could observe fast and get all the benefits of observing fasts generally.
Vyas advised him to observe fast on this day and not to take even a drop of water and all the blessings would come to him.
This day falls during the hottest and driest period of the year.
Bhima did as advised and it is believed that vigorous fast, japa, ritualistic deeds, charity etc. done on this day will prove to be beneficial.