Distilled water is nothing but water. That means it has no ions, no minerals, and no hardness. Without anything to buffer it, the pH is not very stable (although technically neutral at a pH of 7). Distilled water is obtained by distilling (boiling) water and collecting the steam and re-condensing that. Distilled water is NOT safe by itself to be used with animals or for drinking. It will suck the ions out of any animal. Distilled water can be mixed with other waters and used. By mixing it with hard water for example, a water with lower hardness can be obtained. Distilled water is mostly sold for cleaning contact lenses because it is just water. There are a few cases where distilled water can be used as is for animals. Certain crustaceans such as triops and fairy shrimp can be hatched in distilled water.