KCl, also known as potassium chloride, does dissolve in water. According to Everything Science, ionic compounds can dissolve in water because of water's polar nature.
When an ionic compound is dissolved in water, the positive ion of the compound is attracted to the negative pole of water, and the negative ion is attracted to the positive pole of water. KCl becomes K+ and Cl- ions when in water through processes of dissociation and dissolution.
According to ScienceGeek.com, KCl is more soluble than table salt, NaCl, at temperatures above 30 degrees Celsius. According to KnowsWhy.com, KCl's ability to dissolve in water makes it useful in making fertilizer because plants need potassium for growth. In addition to dissolving in water, KCl dissolves in alcohol and other alkali.