Matsya Purana — Description of Gomedaka and Puṣkara Dvīpas; the Lokāloka Boundary; Ocean Tide...
पूर्वार्धे पर्वतस्यापि द्विधा देशस्तु स स्मृतः स्वादूदकेनोदधिना पुष्करः परिवारितः //
pūrvārdhe parvatasyāpi dvidhā deśastu sa smṛtaḥ svādūdakenodadhinā puṣkaraḥ parivāritaḥ //
On the eastern half of the mountain, that region is said to be divided into two; Puṣkara is encircled by an ocean of sweet water.
This verse is not about Pralaya; it belongs to the Matsya Purana’s cosmographic mapping of regions and oceans, describing Puṣkara as surrounded by a sweet-water sea.
Directly, it does not legislate duties; indirectly, such geographical-cosmological knowledge frames Purāṇic ideas of sacred space and pilgrimage, which kings support through protection of routes, tīrthas, and public works.
No explicit Vāstu rule is stated; the key takeaway is sacred-geographical orientation (east/“pūrvārdha”) and the notion of ritually significant landscapes (regions encircled by purifying waters), often used to contextualize tīrtha and temple traditions.