Explanation:

- Option 1: Washington, DC

- This city often hosts significant international events, but it was not the venue for the UN 2023 Water Conference.

- Option 2: New York

- Correct Answer: The UN 2023 Water Conference was held at the United Nations Headquarters in New York, USA. This is a common location for major UN conferences and summits.

- Option 3: San Diego

- San Diego is recognized for environmental events, but it did not host the UN 2023 Water Conference.

- Option 4: New Delhi

- While New Delhi hosts many international conferences, the 2023 UN Water Conference was not held here.