Water chestnut, or singhada, is generally considered acceptable in many Jain diets, because it is not an underground root vegetable like potato, onion, garlic, or carrot.

A simple Jain view is:

• Fresh water chestnut: usually allowed in many Jain households.
• Water chestnut flour: also often used during upvas / fasting.
• However, some Jain traditions or local customs may be stricter, so practice can vary.

So, in short: water chestnut is commonly permitted in Jain diet, but follow your family or temple tradition if they observe stricter rules.