Laser could be aimed at say 30 degrees from vertical onto the waters'
surface, a sensor at 30 degrees the other side of vertical would pick up
specular reflection, BUT:

Water's top surface isn't perfectly flat so you get early "hits",
perhaps want several photodiodes and to think on how to handle the top
surface wave problem there.  If you have a top styrofoam "float" atop
the water, stick a reflective mylar sheet on there and you have specular
reflection again, and reduce the wave problem <G>

There are capacitive sensors used to detect water levels also.

What's wrong with a cheap and easy, hot bead thermistor solution,
though?  Constant current through a thermistor to intentionally
self-heat it to say body temperature or so, when in free air -  then
measure the resulting voltage - when water level rises to where the
thermistor is covered in water, it'll cool the thermistor in a heck of a
hurry, thus voltage change and you know the water's there.  Want the
water to not spray onto the thermistor, of course, placing the
thermistor inside a tube or if needed adding a tank water inlet baffle
will solve that though <G>  Yeah, it's contact sensing, I know.

  Mark

Hugo Jorge M|ller wrote:
> Adam:
>    How work the laser measurement of liquid (water) level ? Do you know
> something that sell this sensores ready to use ?
>
> With respect to wet sand properties, i don't have more information that
> you.. sorry  I am in the beggining of my project and
> recolecting information, I am not a expert on sand and concret ;-)
>
> TIA.
>
> Hugo
<snip>