Our house has a well with pretty hard water in it; we find stuff
precipitating over time in the toilets, etc.  We've got one pipe that's
a particular problem - the hot water pipe to the shower in the
downstairs bathroom.  We don't use that shower often, but both the water
pressure and the temperature of the water coming out seem to be falling
off steeply over the last 5 or 6 months.

   The pressure and temperature of the hot water in the sink in the same
bathroom isn't anywhere near as bad.

   Is there an easy way to tell if this is caused by mineral deposits,
and if so where in the pipe?  It's getting to the point where we
couldn't expect any guests to use that bathroom anymore.

Thanks
-Mark