In Jain practice, the exact rules for fasting (upvas) and ending water depend on the tradition (Digambar vs. Śwetambar) and the type of fast you are observing. Since there can be variations, here is a simple, general guide you can follow, and then you can check your own tradition or with a guru for your specific rules.

• Before starting a fast day:

- Prepare mentally and morally: cleanse the mind, resolve to follow the vow sincerely, and consider doing a short pratikraman or paushadh (reflective rite) if you normally do it on upvas. - Eat a light, sattvik meal before beginning the fast, keeping in mind your capacity and the rules of your tradition. - Avoid foods that are against the vow you’ve taken (eggs, root vegetables if those are part of your upvas restrictions, etc.).

• About ending water (drinking water during the fast):

- Dry fast (nirjala upvas): Many practitioners do not drink any water or food from the moment the fast begins until it ends. The fast typically ends at dawn or after a prescribed period, and water may be resumed after breaking the fast. - Water-permitted fast: Some upvas allow limited water intake or water after a certain time of the day. The exact time and amount depend on your tradition. Commonly, water is resumed only after you have completed the required hours of fasting and performed the closing rites of the day.

• When the fast ends:

- The fast usually ends at dawn (or as prescribed by your guru) with a ritual of closing the vrata (upvas completion), often preceded by a short pratikraman or arati. - After the formal ending, you may drink water and have a light, simple meal, gradually returning to normal eating.

• Important note:

- Because there are distinct rules in Digambar and Śwetambar practices, and because different communities may have local customs, it is best to confirm the exact start and end times and whether water is allowed with your own sect guru or your parish guide before you begin.

If you’d like, tell me whether you follow Digambar or Śwetambar practice and what type of fast you’re planning (dry fast or water-permitted), and I can give a more precise outline according to that tradition.