Lord Vishnu's followers observe Ekadashi vrat. As the name of the festival suggests, Nirjala means fasting without drinking a sip of water. One cannot even have food. Some devotees although have fruits and go for a milk diet. During Nirjala Ekadashi one should wake up early, take bath, wear new clothes. One should also maintain celibacy and also chant OM Namo Bhagavatae Vasudevaya Mantra. You should also make payasam or sheera and focus on doing good deeds.
Doing this vrat is very tough as devotees need to fast for 24 hours and be without food and water. Those who are fit should do this fast and one's having medical issues should avoid.
Nirjala Ekadashi: History and Significance
The day started when Bhima was unable to fast and was upset due to his weak determination. He thought that he had disrespect Lord Vishnu and so met Maharishi Vyasa, who told him to keep a single Nirjala Ekadashi fast. The festival is also known as Bhimseni Ekadashi or Bhima Ekadashi.