Me searching again

I am looking for a reliable way to detect water, although the sensor is=
 covered with a layer of dirt, oil film, etc.  And the water may be pure or=
 contaminated.
(=3Dnot possible to use electrodes or optics, and capacitive is not reliable=
 for pure water, as the dirt may conduct better...  Other ideas are welcome!=
 )

My idea is to place two small piezo crystals with some mm gap between.  The=
 gap is to be wide enough to the dirt don=B4t bridge all over it.  Then when=
 water arrives it fills the gap and acousticly couples the piezos.

Normal piezo speakers are too wide to fit, and probably to fragile.  I think=
 a more cubic formed multilayer piezo would be better.

On my table i have a nice pamphlet from Philips showing exactly what i want=
 :)
...but when i call them they say piezos was dropped or sold off years ago :/

So... anyone have an idea of where to find such cuties?

/Morgan=20

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