I am on the do not call list and this number keeps coming up. I called it back and it is soliciting something for water

They called on Jan 5 2009

I just got a call about water quality in our area and would I rate it.  It sounded like 2 female teenagers playing around and was hard to understand..there was laughing and then they hung up.

Said they were doing a water quality survey. However, by the questions they were asking, I think they are from some sort of company selling water conditioners or purifiers.