आपः पीतास्त्रेधा विधीयन्ते तासां यः स्थविष्ठो धातुस्तन्मूत्रं भवति यो मध्यमस्तल्लोहितं योऽणिष्ठः स प्राणः ॥ ६.५.२ ॥
āpaḥ pītāstredhā vidhīyante tāsāṃ yaḥ sthaviṣṭho dhātustanmūtraṃ bhavati yo madhyamastallohitaṃ yo’ṇiṣṭhaḥ sa prāṇaḥ || 6.5.2 ||
2. When we drink water, it becomes divided in three parts. The grossest part of it becomes urine; that which is less gross becomes blood; and the finest part becomes prāṇa, the vital force.
Āpaḥ, water; pītāḥ, when drunk; tredhā, in three ways; vidhīyante, is divided; tāsām, of it; yaḥ sthaviṣṭaḥ dhātuḥ, that which is the grossest part; tat mūtram bhavati, that becomes urine; yaḥ madhyamaḥ, that which is less gross; tat lohitam, that [becomes] blood; yaḥ aṇiṣṭhaḥ, that which is the finest part; saḥ prāṇaḥ, that is prāṇa.
Water also has a threefold function. When we drink water, the grossest part of it flushes our whole system and at last passes out of the body as urine. Then that which is less gross becomes blood. If I do not drink water, the blood would clot and there would be no more blood supply. Then the finest aspect becomes prāṇa, the vital force. Without water, we could not breathe or live.