Approximately how many showerheads are there in United States homes, and
what percentage of them are "clogged" with lime scale to the extent
that the user must either clean them regularly (by what method), or
replacd them periodically and, if so , how often?

When these numbers are available, that will pretty much indicate that
there are too many people in the survey business and that they have
run out of questions and are just grasping at straws to keep their
jobs.

To nelson-ga:  A non-clogging showerhead product I have created could
save countless acre feet of water and mlllions of showerheads from
becoming land fill if it comes on market, not to mention restoring
showering pleasure to millions of people plagued with lousy clogged-up
showerheads.   I am seeking a company to manufacture and distribute my
novel product, and none will do so if they do not have answers to the
questions I posed.  Please reconsider your take on this matter, and
note that I upped the ante.

I'm not a researcher here anyway, so feel free to ignore me.  You
upped the ante incorrectly.  You should have edit this question, not
posted a new one.

Eezarf, you could offer a $75 tip for a highly satisfactory answer.
This way all the extra money goes to the Researcher who answers. By
making the question $100, you are giving Google more money.

You may want to also have research done on hard water areas as these
are more likely to need such a product such as that you have come up
with. Either determining who has hard water or where the most water
softeners are sold could point you in the right direction for more
information.

Neither I nor anyone I know has ever had a problem with clogging
showerheads. I have seen CLR advertised as a way to clean
scale-clogged showerheads, however. Maybe they can help you, too.