अथ यत्रैतत्पुरुषः पिपासति नाम तेज एव तत्पीतं नयते तद्यथा गोनायोऽश्वनायः पुरुषनाय इत्येवं तत्तेज आचष्ट उदन्येति तत्रैतदेव शुङ्गमुत्पतितं सोम्य विजानीहि नेदममूलं भविष्यतीति ॥ ६.८.५ ॥
atha yatraitatpuruṣaḥ pipāsati nāma teja eva tatpītaṃ nayate tadyathā gonāyo’śvanāyaḥ puruṣanāya ityevaṃ tatteja ācaṣṭa udanyeti tatraitadeva śuṅgamutpatitaṃ somya vijānīhi nedamamūlaṃ bhaviṣyatīti || 6.8.5 ||
5. Then when a person is said to be thirsty, it is to be understood that the water he drank has been carried away by fire. Just as people refer to a leader of cows, or a leader of horses, or a leader of people, similarly, people say that fire is the leader of water. So also, O Somya, know that this sprout [i.e., the body] is the product of something [i.e., of food and drink]. It cannot be without a root.
Word-for-word explanation:
Atha, next; yatra, when; puruṣaḥ, a person; pipāsati etat nāma, is said to be thirsty; tat, then; tejaḥ eva pītam nayate, fire has earned away [the water that he drank]; tat yathā, just as, for example; go-nāyaḥ, a leader of cows; aśva-nāyaḥ, a leader of horses; puruṣa-nāyaḥ, one who leads other people; iti, these terms people use; evam, similarly; tat tejaḥ, that fire; ācaṣṭe, is called; udanyā iti, the leader of water; tatra, so also; vijānīhi, know; somya, O Somya; etat eva śuṅgam, this sprout [i.e., the body]; utpatitam, is produced [by something]; idam, it; amūlam na bhaviṣyati iti, is not without a root.
Commentary:
When does a person feel thirsty? When there is a shortage of water in his body. How does this shortage occur? It occurs when the heat in the body turns the water into blood and other things. As soon as the water is consumed in this way a person feels that he has to drink more water.