Here is a simple Jain view on Upvas without water (nirjala upvas / Tivihar upvas pachkan):

• What it means: A waterless fast where you abstain from food and from drinking any water. The vow (pachkan) sets the rules for the day, often including doing Samayik and Pratikraman along with Upvas. In some Jain traditions, a very small amount of boiled water may be permitted, but the core idea is to refrain from drinking plain water and eating solid foods for the chosen period. ( jainknowledge.com)

• How long: Typically from sunrise to the next sunrise (about 24 hours), though practices can vary by local tradition and guru guidance. The pachkan is recited at the start to declare the boundaries of the fast. ( jainknowledge.com)

• What you do during: After taking the pachkan, the focus is on discipline and purification—often including Samayik (meditative reflection) and Pratikraman (repentence and reflection), with strict avoidance of food and water as defined by one’s capacity and vow. ( jainknowledge.com)

• Breaking the fast: The fast is broken with a mindful, gradual return to eating and drinking, following the same respectful mindset with forgiveness for any inadvertent faults during the fast. The exact breaking practice can vary by tradition. ( jainknowledge.com)

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