Unless you live in the sahara desert it shouldn't need water everyday.Impatients generally show you they need water by their leaves drooping.I think you're killing it with kindness!! Don't water it again until you see the leaves drooping.JMO
Kathi

This sounds very suspect for a disease called downy mildew. Since it has been almost 2 months from your post, did the other impatiens in your planters eventually drop their leaves as well? If you still have any plants left with leaves, turn some leaves over (in particular any that may appear yellow) and look closely for a white, downy-like growth on the underside of the leaves. I would be very interested in knowing what you see and geographically where you are located.