Short answer: Not the whole 24 hours. In Ekashana you eat once in the day; water is kept very restrained.

General guidance followed in Jain traditions:

• Only boiled and well‑filtered water.
• Daytime only; avoid water after sunset.
• No juices, milk, tea, or other liquids—only water.
• Keep the number of water-intakes minimal to reduce himsa.

By tradition:

• Shvetambar (Ekasana): You may take boiled, filtered water during the day as needed, but sparingly and not at night. Many observe fixed, limited “water-times.”
• Digambar (Ekabhukta): Stricter form prefers taking water with the meal only; if needed for health, small amounts of boiled, filtered water may be taken in the daytime, but avoided at night.

If you are observing under a specific guru/sect, follow the discipline they prescribe.