Śaṅkaraon Brahma Sūtra 3.1.3

Scripture states that, when a new body is obtained, the prd«as also go (from the old body to the new one). Cp. ‘When he thus departs the (chief) pra;/a departs after him, and when the prawa thus departs all the other prfxwas depart after it ’ (Bn. Up. IV, 4, 2), and similar passages. Now this going of the pra;^as is not possible without a base ; hence we infer that water also—mixed with parts of the other elements—goes (from the old body to the new one), serving the purpose of supplying a base for the moving prAwas. For the pra;/as cannot, without such a base, either move or abide anywhere ; as we observe in living beings.