The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
11. Water (is produced from fire).
We have to supply from the preceding Sûtra the words 'thence' and 'for thus the text declares.'--Water is produced from fire; for the text says, 'it sent forth water' (Kh. Up. VI, 2, 3), and 'from fire (sprang) water' (Taitt. Up. II, 1). These explicit statements allow no room for doubt 2. The Sûtrakâra, however, having explained the creation of fire, and being about to explain the creation of
earth, propounds this Sutra in order to insert water (and thus to point out its position in the srishtikrama).
22:2 So that the Sutra might possibly be looked upon as no called for.