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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.
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.
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.
— 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.