In Jainism, during Ekasana (taking only one meal a day), the rules about water intake often depend on the specific tradition or sect (Shwetambar or Digambar) you follow, as well as the level of austerity you wish to observe.

Common practice (especially among Shwetambar Jains):

• On the day you are observing Ekasana, you should avoid taking water after sunset (pradosh kaal) on the previous day, and continue to avoid water until you finish your Ekasana meal the next day.
• After completing your Ekasana meal, you may drink water until sunset, after which you abstain again.

For higher austerity or during Paryushan:

• Some may choose to avoid water (boiled or otherwise) from sunset on the previous day until after completing Ekasana the next day, or even until the next sunrise.

Summary:

• Start avoiding water at sunset today if you plan to do Ekasana tomorrow, in keeping with typical Jain practice.
• Resume water intake after your Ekasana meal, but before sunset the same day, if your tradition allows.

Please consult your local Jain priest or elders for the specific practice followed in your tradition or community, as customs can vary.