In Jainism, ekasana refers to taking only one meal in a day, often observed as a vrata (vow) for spiritual discipline. Chauvihar means refraining from eating or drinking anything after sunset until the next sunrise.

If you are not doing chauvihar on the previous day of your ekasana, traditional Jain practice allows you to drink water even after sunset, up until you sleep, or as per your usual routine. There is no strict rule in Jainism that forbids drinking water till 11:59 PM on the previous day of ekasana if you are not observing chauvihar.

However, the most ideal practice, especially among stricter followers and monks, is to stop consuming food and water after sunset. For householders, the practice can be more lenient, and it is acceptable to drink water after sunset if you are not observing chauvihar.

Summary: Yes, according to Jain household practices, you may drink water till 11:59 PM on the previous day of ekasana if you are not observing chauvihar. However, for greater spiritual benefit and in line with Jain principles, it is encouraged to gradually adopt chauvihar if possible.