Nirjal upvas means a waterless fast. In Jain practice, the duration is not fixed and depends on one’s vow taken with guidance from a guru or spiritual teacher.

• Common durations for lay practitioners: 1 day, 3 days, 7 days. Some may undertake longer fasts like 11 days depending on the vow, the occasion, and their readiness.
• Among serious ascetics or very strict observers, longer Nirjal fasts (e.g., 11, 21 days) are possible, but those are not typical for most lay followers.

Key points:

• It is a solemn vow taken with discipline and proper preparatory rites.
• It should be undertaken only with careful self-assessment and guidance from a qualified Jain teacher.
• The specifics can vary between Digambar and Shwetambar communities and according to the particular spiritual goal or festival.

If you’d like, tell me your tradition (Digambar or Shwetambar) and whether this is for a lay observance or a more strict ascetic practice, and I can outline more precise, tradition-specific guidelines.