Similar to ionic salts, a zwitterion in the absence of a polar solvent like water, is in the solid form. NaCl is one example. But the moment you dump NaCl into a liquid, it dissociates for the more favorable attraction with water.
http://www.chemguide.co.uk/organicprops/aminoacids/background.html
"Amino acids are generally soluble in water and insoluble in non-polar organic solvents such as hydrocarbons.
This again reflects the presence of the zwitterions. In water, the ionic attractions between the ions in the solid amino acid are replaced by strong attractions between polar water molecules and the zwitterions. This is much the same as any other ionic substance dissolving in water.
The extent of the solubility in water varies depending on the size and nature of the "R" group."