Tonic water is known for its bitter taste and it usually comes into use when mixing up cool cocktails. The tonic water owes its bitter taste to the special ingredient called quinine which is dissolved in it. Drinking such water with high percentage of quinine has proven to be one of the most effective treatments against the deadly disease malaria.
It was first discovered by the indigenous Quechua tribes from Peru and Bolivia who used the medicinal properties of quinine which could be found when you peel off the bark of the chinchona tree. Although you can treat malaria with strong tonic water with high percentage of quinine you can also perform a somewhat entertaining bar trick with it.
Quinine is actually utilized in photochemistry. When the special ultraviolet light emitted from a black lamp hits the tonic water it interacts with the phosphor contained in quinine therefore your water glows. It is perfectly safe to drink glowing tonic water and it looks very cool and entertaining.