Zwitterions are generally soluble in water at any pH.

At physiological pH, zwitterions exist with a zero net charge because their positive and negative charges cancel each other out. Water has a slight positive charge near its hydrogen atoms and a slight negative charge near its oxygen atom. When a zwitterion is put in water, the ionic attractions between ions in the zwitterion are replaced by strong attractions between the polar water molecules and the neutrally charged zwitterion. This strong attraction between water and the zwitterion generates enough energy to pull the zwitterion’s ionic lattice apart, result in it getting dissolved in water.