In this context water immersed carbon nanotubes (CNTs) may act as an ideal optoacoustic source, due to their nanometric radial dimensions, peculiar thermal properties and broad band optical absorption.  We show that, depending on the combination of CNT size and laser pulse duration, the CNT can act as a thermophone or a mechanophone.  As a thermophone, the CNT acts as a nanoheater for the surrounding water, which, upon thermal expansion, launches the pressure wave.  As a mechanophone, the CNT acts as a nanopiston, its thermal expansion directly triggering the pressure wave in water.  This is at variance with respect to the commonly addressed case of water-immersed single metallic nano-objects excited with ns laser pulses, where only the thermophone effect significantly contributes. 
THERM