Matsya Purana — Catalogue of the Eighteen Puranas
यत्र ब्रह्मवराहस्य चोदन्तं वर्णितं मुहुः तदष्टादशसाहस्रं ब्रह्मवैवर्तमुच्यते //
yatra brahmavarāhasya codantaṃ varṇitaṃ muhuḥ tadaṣṭādaśasāhasraṃ brahmavaivartamucyate //
That Purāṇa in which the account of Brahmā’s Varāha (the Boar incarnation) is repeatedly described—consisting of eighteen thousand verses—is called the Brahma-vaivarta (Purāṇa).
This verse does not directly describe pralaya; it catalogs Purāṇic literature by identifying the Brahma-vaivarta Purāṇa through its recurring Varāha narrative and its stated length (18,000 verses).
Indirectly: it supports dharma-study by pointing to authoritative Purāṇas. For kings and householders, such cataloging guides which texts to consult for vrata, dāna, and ethical instruction, though no specific rājadharma or gṛhastha-rule is stated here.
No vāstu/temple-building rule is taught in this verse; its ritual significance is bibliographic—naming and characterizing a Purāṇa used as a source for ritual narratives and theological themes (e.g., Varāha).