In Jain dharma, root vegetables are generally avoided because uprooting them harms life forms in the soil. Water chestnut (singhara) is not a root vegetable; it is the seed of an aquatic plant. Because of that, many Jain authorities treat it as permissible (bhaksya) to eat.

However, practices can vary slightly between Digambar and Shwetambar traditions and among different communities. If you follow a specific local guidance, that should be the guiding rule.