Given
Density of liquid water = 1.0g $cm^{-3}$
Density of water vapour = 0.0006g $cm^{-3}$
Mass of 1000mL stream = $1000\times0.0006 = 0.6g$
Since, Volume of liquid water = $\large\frac{\text{Mass of 1000mL stream}}{\text{Density of liquid water}} = \large\frac{0.6g}{1g\;cm^{-3}}$
$\therefore$ Volume of liquid water = $0.6 cm^3$
Hence answer is (c)