Matsya Purana — Vrata-Ṣaṣṭhī: The Sixty Sacred Vows
निशि कृत्वा जले वासं प्रभाते गोप्रदो भवेत् वारुणं लोकमाप्नोति वरुणव्रतमुच्यते //
niśi kṛtvā jale vāsaṃ prabhāte goprado bhavet vāruṇaṃ lokamāpnoti varuṇavratamucyate //
Having spent the night dwelling in water, one should, at dawn, give a cow in charity. He attains Varuṇa’s realm; this observance is called the Varuṇa-vrata (vow of Varuṇa).
This verse is not about Pralaya; it teaches a ritual vow (Varuṇa-vrata) where water-austerity and cow-donation lead to attaining Varuṇa’s realm.
It frames dharma as disciplined observance and charity: a householder (and by extension a king) practices restraint (night in water) and public beneficence (go-dāna) to gain religious merit and auspicious posthumous attainments.
The significance is ritual, not architectural: a prescribed vrata-vidhi involving nighttime water-dwelling (austerity/purification) followed by dawn-time cow donation, culminating in the promised fruit of reaching Varuṇa-loka.