Above: A Garden wall.Typical place for efflorescence, and not necessarily unattractive, depending on your point of view.
A balcony wall: also a place where water collects and drips down. This is a brand new house, so stucco does not have to be very old for this to occur.
Old La Habra stucco, a garage wall where there are holes in the overhanging roof and the water drips down.
It is the growth of salt crystals on the surface, due to the evaporation of salt laden water, a flowering, or blooming powdery crystalline deposits. This condition may appear during wet weather or when a concrete masonry surface receives water from a concentrated source, such as a sprinkler.
When this condition occurs on stucco, it is important to realize that the white crystalline bloom is not the result of faulty stucco or improper application by the plastering contractor, but rather a deposit of mineral salts from a variety of possible sources."
-- from a La Habra brochure
For what to do about efflorescence, see this link:
http://lahabrastucco.com/stucco_faq.htm