Rudra-prasava-varṇana
The Manifestation and Naming of Rudra / Nīlalohita
तस्मान्मूत्रं पुरीषं च नाप्सु कुर्वीत कर्हिचित् / न निष्ठीवेन्नावगाहेन्नैव गच्छेच्च मैथुनम्
tasmānmūtraṃ purīṣaṃ ca nāpsu kurvīta karhicit / na niṣṭhīvennāvagāhennaiva gacchecca maithunam
Therefore one should never urinate or defecate in water; one should not spit into it, not bathe by submerging, and not engage in sexual union near it.