Distilled water produced an unrippled, carrot-shaped icicle. When the scientists added a pinch of sodium chloride, or table salt, regularly spaced ripples formed. When they added more, the ripples became wildly irregular.From a study published in the New Journal of Physics, via Science News and Boing Boing.
The researchers have not been able to find a theory to explain why salt is crucial to ripple formation. Fortunately, nature doesn’t need a theory; the team found that water running off Toronto roofs had enough dissolved ions to make ripples on its own.