In strict Jain practice, avoid eating underground edible parts because they involve uprooting life forms. Water chestnut is an aquatic tuber-like part of the plant, so many Jains consider it unsuitable to eat. If you follow a more lenient household tradition, you might differ, but the common guidance is to refrain.

If you’d like, I can look up specific Jain scholarship or ritual guidance on this from Jain Knowledge sources.