Ekadasi fasting is dedicated to Hindu God Vishnu and is observed on the 11th day of a lunar fortnight as per traditional Hindu calendar. A specific period during Ekadasi fasting is considered highly auspicious and this is the Harivasaram period and is strictly followed by many Hindus in South India . The timing of Harivasaram is based on Tithi in Hindu calendar.
The last one quarter of Ekadasi tithi (11th day) and the first one quarter of Dwadasi tithi (12th day) is known as Harivasaram. Those people strictly following Harivasaram can see it marked in their local Panchangs.
A complete fast is observed during the period – not even water is taken by devotees during Harivasaram.