If by “tevyar” you mean “tivihar (trivihar) upvās”:

• Meaning: Tivihar upvās is a fast in which one abstains from all food and takes only boiled, filtered water. It is lighter than chovihar (where even water is stopped after sunset).

• Why water is allowed:

1) Ahimsa care: Boiling and filtering water reduces living organisms in it, so drinking such water causes far less himsa than taking any food or unfiltered liquids. 2) Health support: Austerity should aid inner purity, not harm the body. Limited water prevents dehydration so the vow can be sustained with steadiness. 3) Scriptural practice: Jain conduct texts permit mendicants and laypeople to drink only boiled, properly filtered water within prescribed times. This is seen as a minimal, necessary support to sādhanā, not an indulgence.

• Time rules (traditions/community practice):

• Shwetambar: On a fasting day, only boiled, filtered water is taken during daylight (from after sunrise until before sunset). Ideal is no water at night (that is chovihar). • Digambar: The stress is also on carefully filtered water and restraint; details of timing can vary by ācārya’s code and local ācāra. • Many communities keep a strict daytime window; some allow exceptions for health under guidance.

Essence: Water is allowed in tivihar because it is the least-harm, minimal support for the body, prepared to avoid himsa, so the primary aim of the fast—self-restraint and inner purity—can be maintained.