Bhashya
तथा आपः ।अध्यात्मं रेतसि अपां विशेषतोऽव-स्थानम् ॥
In plain words
Water works the same way. In your own body, water's special home is the vital seed.
Close to the Sanskrit
Likewise [for] water. Within the body, the particular seat of the waters is in semen.