Markandeya Purana — Adhyaya 32, Shloka 16
Adhyaya 32 — Rules for Parvana Śrāddha: Foods that Please the Ancestors and Items to Avoid
न लभेद्यत्र गौस्तृप्तिं नक्तं यच्चाप्युपाहृतम् ।
यन्न सर्वापचोत्सृष्टं यच्चाभोज्यं निपानजम् ॥
na labhed yatra gaus-tṛptiṃ naktaṃ yac cāpy upāhṛtam / yan na sarvā-paco'tsṛṣṭaṃ yac cābhojyaṃ nipānajam
凡牛亦不能满足而安饮之处之水，不可用；夜间取来之水，不可用；非由“完备称职之厨者”所放出、未依法妥善处理之水，不可用；饮水处/槽中不堪饮用之水，亦不可用。
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FAQs
Purity is validated by practical signs: if even a cow avoids it, humans should not offer it in sacred rites. The verse also discourages careless procurement (night fetching) and unclean communal sources.
Dharma/ācāra guidance (ritual procedure), outside the pancalakṣaṇa core.
The ‘cow test’ makes nature a witness to purity. The Pitṛ-offering is ideally aligned with ṛta (order); unsuitable water symbolizes disorder entering the rite.