In Jainism, particularly among Shwetambar sects, boiled water (ushnodaaka) is consumed to minimize harm to microscopic life (nigod jivas) present in untreated water. During ekasana (the practice of eating one meal a day, usually before sunset), there are specific rules about when boiled water can be started:

Boiled water is generally allowed to be consumed from the day after Ashadha Shukla Purnima (the full moon day of the bright half of the Ashadha month) until the end of Kartik Shukla Purnima (the full moon of the bright half of Kartik). This period roughly coincides with the monsoon season in India, when the proliferation of microorganisms in water is highest.

Summary of the timing:

• Start: The day after Ashadha Shukla Purnima
• End: Kartik Shukla Purnima

Outside of this period, in some traditions, boiled water may not be consumed, or the rules are stricter; always follow the guidance of your local Jain sangh or guru for specific practice.

Note: These practices may slightly vary by sect and local tradition, so it’s best to consult with your community or spiritual teacher for precise observance.