You mean one of these?

http://www.terranovatunes.com/instrmet.html

Waterphon or Oceanharp
An acoustical friction instrument that sounds like a synthesizer. Filled with water it produces a magical sound reminiscent of whales. It can be held by the handle or hung from a strap. Played with either a bow or mallets for a combination of different tones.

These have been around for several decades. I've seen and heard legit pieces of music that require these instruments in the score.

Ah yes, the good ol' Waterphone.  Great piece of symphonic band music utilizing this instrument (Briefly and non-specifically) called "Ghost Train" by Eric Whitacre.

Lesser known facts,
It is believed that if you go into the ocean with a waterphone and play it underwater, you can call whales with it.  Haven't tried it, plus the saltwater will murder the sensitive metals inside the WP, but you can clean it out.  Very intriguing instrument, albeit too expensive and too impractical for some nerd percussionist to want to specialize and be a "Solo Waterphonist", but then again they said the Theremin was impractical yet you could play Bach on it.  Go figure.

ive been into the waterphone sound for a bout a year now, anyone know just how pricey these things are for sure?

I guess I do not want one after all!  

as i was saying, actual "waterphones" are pricey, but lark in the morning has a very nice quality version for much less

second item down

larks "oceanharp" only comes in one size, waters makes a few sizes, but you most certainly pay for 'em.