Answer

In Jain Dharma, water chestnut can be acceptable or not acceptable depending on what exactly is meant by “water chestnut.”

• If it refers to Singhara / water caltrop — the fruit that grows in water — many Jains consider it acceptable, especially during fasting-related foods, if it is properly cleaned and prepared.
• If it refers to a root/tuber-like item taken from under the mud or plant base, then it may be avoided under Jain dietary discipline.

Explanation

Jain food rules generally avoid:

• Root vegetables, because uprooting them destroys the whole plant and may harm many tiny living beings.
• Foods with high possibility of minute organisms, decay, or contamination.

The common Indian Singhara is generally treated as a fruit/nut from an aquatic plant, not like potato, onion, garlic, carrot, etc. Therefore, many Jain families allow singhara flour during certain observances.

However, practice may vary by family, sampraday, and level of strictness.

Spiritual Understanding

The main Jain principle is Ahimsa — minimizing harm to living beings. So the decision should be made not only by name, but by understanding:

• What part of the plant is eaten
• How it is harvested
• Whether it involves unnecessary destruction or many tiny lives

Takeaway

If by water chestnut you mean Singhara, it is commonly accepted by many Jains. But if you follow strict household or temple dietary rules, it is best to follow your family/guru’s guidance.