Short answer: It depends on your vowed discipline and local sangh guidance.

• As a fruit, lemon itself is not a root (kand) and is generally permissible.
• But if you have taken the boiled-water-only vow (very common in Paryushan), do not add lemon to water. Adding anything after boiling breaks the “boiled water only, taken in daytime” rule.
• Many observe extra simplicity by avoiding sour/pungent tastes during these days; in such practice, lemon is avoided.
• Shwetambar Paryushan: often no green leafy vegetables and very simple, non‑stimulating food; some families also avoid sour items like lemon.
• Digambar Das‑Lakshan: usually even simpler food/boiled‑water discipline; sour add‑ons like lemon are typically avoided.

Best practice: If your pachchakkhan (vow) or temple guidelines are stricter, avoid lemon. If not, lemon used in simple, freshly cooked food is generally acceptable—but never in boiled water.

For simple food rules of Paryushan, see: and fasting rules here: