When we say water purity, what do you think?
‘Ehh… how pure the water is?’
However, if to think deeper, it is actually hard to define purity.
Water purity is a complex term to understand clearly. Are we talking about water contamination? Are we talking about pollution? In the United States, the EPA defines "pure" water as water free from all types of bacteria and viruses. But there is more to purity than just that.
Water is a compound made up of hydrogen and oxygen, so pure water would be water that contains nothing but hydrogen and oxygen. However, pure water of this sort does not normally exist except in the controlled environment of a laboratory. Even in a laboratory pure water is hard to come by. For example, bacterial contamination of purified water can cause major problems in the laboratory. Even if organic and inorganic chemical impurities are removed down to the limits of detection, bacterial growth can still occur, even though very pure water provides an extremely harsh environment with apparently negligible nutrient content. To avoid metallic contamination of the water, laboratory water purifiers are constructed using plastics. The bacteria can use these materials that are in contact with the pure water as a carbon food source to sustain them, and then when they die they release further contaminants into the water. If this bacterial growth is not minimized, it can cause significant difficulties in the day-to-day operation of the laboratory.
From a drinking water standpoint, most references to "pure water" are in relation to bacteria content and not the chemical contaminant concentrations. The bacteria in pure water themselves are not the only problem; they also produce endotoxins and nucleases. Endotoxins are fragments of Gram-negative cell membrane that are released during bacterial cell metabolism, and are also produced at the death of Gram-negative cells.
Endotoxins — the most common pyrogens — are powerful immune stimulants, raising temperature if they are injected into the bloodstream. This can even lead to Gramnegative sepsis and death. Ultraviolet irradiation is also very effective at destroying micro-organisms. Although it is not a barrier process, relatively low energy doses of ultraviolet light greatly reduce overall bacterial levels, minimizing the challenge on downstream purification processes.
There’s no such thing as pure water. The very concept of ‘pure’ water is misleading. Pure water does not exist in nature. Water is the universal solvent. Even as it falls to earth as rain it picks up particles and minerals in the air. And as soon as it hits the ground it captures minerals from the soil and rock upon which it lands. It makes its way into streams and rivers, carrying soil from the mountains to the sea. Water picks up contaminants such as airborne mercury while it’s falling as rain.
Consumers can achieve healthy water by identifying the unhealthy contaminants in their water and then taking action to remove them. In general, the public discussion about water can and will switch from the notion of ‘pure’ to ‘healthy’. Healthy water is attainable, whereas pure water is not. And just what is healthy water? Healthy water can have an optimum pH of 7.2 to 7.6. Harmful contaminants such as chlorine, chloramines, disinfection by-products such as the trihalomethanes, and any harmful chemical or metals whether man made or naturally occurring have been identified and removed with the appropriate treatment.