What type of water does not contain any other substances?

Distilled water is the most purified form of water, as it has undergone a process of distillation, where water is boiled to produce steam, and then the steam is condensed back into a liquid. This process effectively removes impurities, minerals, and other substances, resulting in water that is free from dissolved solids and contaminants. Because of this high level of purification, distilled water is often used in scientific and medical applications where the presence of other substances could interfere with results or processes.

In contrast, tap water typically contains various minerals and chemicals added for safety and taste, such as chlorine, which makes it unsuitable for classification as pure water. Hard water is characterized by high levels of calcium and magnesium, which contribute to its mineral content. Likewise, mineral water is sourced from springs and contains dissolved minerals, which can contribute to flavor and health benefits. Thus, among the options provided, distilled water is the only type that consists purely of H2O, with no other substances mixed in.