I have some white residue building up on the rim of my impatiens clay pot. I'm not sure what it is but it looks like calcium deposit that you'd see in your shower. It isn't appearing on my plastic pot which I water the same way. I'm only using tap water on the plant. But what I don't understand is why its forming on the OUTSIDE of the pot? I just potted this plant like a week ago.

http://www.prism.gatech.edu/~gte385u/pics/impatiens001.jpg

any help would be appreciated.

thanks

steve