Chlorine: The greenish-yellow, highly reactive and diatomic gas that is almost never found free in nature by itself. Most Chlorine is commercially produced and is most widely known for being used within compounds to purify water and create cleaning products.
Chloride: The negatively charged ionic form of Chlorine. Since Chlorine is found deep within the Earth’s crust, and is extremely reactive, the only way it can be found in nature is when it reacts with other chemicals and creates compounds. Chloride is what is created when Chlorine gains an electron and combines with other elements. Chloride is found abundantly in nature and is most commonly known for forming neutral salts such as sodium chloride (table salt), potassium chloride, and calcium chloride.
If you see levels of chlorine in your water, you may be near a water treatment plant, or close to someone dumping pool water.