In Jainism, "Ekashna" (also spelled "Ekashana" or "Ekashan") refers to the practice of eating only one meal a day, typically observed by ascetics and some lay followers as a form of self-discipline and spiritual purification.

Regarding water during Ekashna:

• Traditionally, during Ekashna, one takes only a single sitting of food (meal) during the day.
• Water is generally permitted, but with restrictions. It is ideal to drink boiled and filtered water (known as "ushnodaak" or "boiled water") to minimize harm to micro-organisms, in accordance with the principle of ahimsa (non-violence).
• Some stricter practitioners may limit water intake to only during the meal, while others may allow boiled water throughout the day.
• During more rigorous fasts (such as Upvas or Chauvihar), water intake may be further restricted (for example, no water after sunset or after the last meal).

Therefore, on Ekashna, you may drink water, but it should ideally be boiled and filtered, and the amount and timing may depend on your level of observance and the guidance of your Jain spiritual teacher (Guru).

If you follow a particular Jain sect (Shwetambar or Digambar), practices may vary slightly. It is always best to consult with a knowledgeable Jain monk, nun, or elder for specific guidance according to your tradition.