Matsya Purana — Cosmography of Śākadvīpa and Successive Dvīpas: Mountains
तत्रापि नद्यः सप्तैव प्रतिवर्षं हि ताः स्मृताः द्विनामवत्यस्ताः सर्वाः सर्वाः पुण्यजलाः स्मृताः //
tatrāpi nadyaḥ saptaiva prativarṣaṃ hi tāḥ smṛtāḥ dvināmavatyastāḥ sarvāḥ sarvāḥ puṇyajalāḥ smṛtāḥ //
There too, the rivers are remembered as just seven in each varṣa, recurring year after year. All of them bear double names, and all are regarded as waters of sacred merit.
It does not describe Pralaya directly; it focuses on sacred geography—identifying a traditional set of seven rivers whose sanctity is affirmed as perennial (recognized year after year).
It supports dharma through tīrtha-practice: a householder (and a king guiding public religion) gains and promotes merit via reverence for holy rivers—especially ritual bathing and pilgrimage to acknowledged sacred waters.
Ritually, it highlights puṇya-jala—waters suitable for स्नान (bathing), तर्पण (offerings to ancestors), and purification rites; it does not give specific Vāstu or temple-building rules in this verse.