Short answer

• Best practice in Jain Dharma: after evening Pratikraman, do not take any food or water until the next sunrise.
• If your tradition allows an exception: only boiled and filtered water may be taken for up to 48 minutes (one muhurt) after sunset; after that, avoid water for the night.

Details by tradition

• Shwetambar (common lay practice): After Sandhya (evening) Pratikraman, stop all intake for the night. Where a leniency is followed at home, only boiled-filtered water within 48 minutes after sunset is allowed; then nothing for the rest of the night.
• Digambar (common lay practice): After sunset, no eating or drinking at night. In unavoidable situations only, some accept minimal boiled-filtered water soon after sunset, but ideal is none.

If you did morning Pratikraman: you may drink water after Navkarsi, i.e., 48 minutes after sunrise.

Reason The restraint after Pratikraman protects the vow of avoiding harm to subtle beings active at night and preserves the purity of repentance taken during Pratikraman.