Abstract: An automatic resetting apparatus for a water sound-source which apparatus includes a source of high pressure resetting liquid, conduit means for connecting the source to the sound-source, a valve in the conduit means, which valve is, in use, under the direct or indirect influence of an actuating pressure of a sound source charging fluid, is actuable from a first position to a second position at a predetermined low actuating pressure within the charging fluid and will remain in said second position until the pressure within the charging fluid falls to said predetermined low pressure, whereupon the valve returns to the first position, the second position allowing the resetting liquid to pass along the conduit means to reset the sound-source and the first position allowing discharge of the resetting liquid from the sound-source after the sound-source has been reset.