Bhashya
तथा आपः पीताः त्रेधा विधीयन्ते ।तासां यः स्थविष्ठो धातुः, तन्मूत्रं भवति, यो मध्यमः, तल्लोहितं भवति ; योऽणिष्ठः, स प्राणो भवति ।वक्ष्यति हि - 'आपोमयः प्राणो नपिबतो विच्छेत्स्यते' इति ॥
In plain words
In the same way, water that is drunk divides itself threefold. Its grossest part becomes urine, its middle part becomes blood, and its subtlest part becomes the vital breath. As the scripture will declare: 'The vital breath is made of water; for one who does not drink, it will be cut off.'
Close to the Sanskrit
Likewise, waters drunk are divided in three ways. Of them, whatever is the grossest constituent, that becomes urine; whatever is the middle, that becomes blood; whatever is the subtlest, that becomes prana. For it will say: 'The prana is made of water, of one not drinking it will be cut off' thus.