Each water type has its own level of purity. All types of water from Type I water (ultrapure) to Type IV water (semi-pure) is definedby the ASTM International* standard to have certain characteristics of resistivity (measured in Ω-cm) or conductivity (measured in µS/cm), which reveals inorganic impurities. Type I water is furthermore defined by its TOC (total organic compounds) purity, measured in parts per billion.
Using the right water type in your laboratory is important. To avoid wasted work, ruined results or sullied samples, make sure your laboratory is using a water type with the appropriate purity level for your particular application.
Don't go overboard and use water that's too pure for your needs, either; that mistake could cost cash and resources better spent on research.
Below is an explanation of the differences among laboratory-grade types of water, including common applications to which they're conducive, and available dispensing methods.
Contaminants in water can include particulates, dissolved organics, dissolved inorganics, microorganisms and/or pyrogens. To the varying degrees mentioned, the following key water types have such contaminants removed to produce water of application-specific quality**.
For large laboratories, such as university or pharmaceutical research buildings, large water purification units are often necessary. To meet the varying needs of the researchers utilizing multifunctional laboratory spaces, a substantial water purification system may produce RO, DI or Type III water that is then held in a reservoir tank for a specified period of time until it is needed. (This feed water can also be pumped to locations within laboratories with large-scale water requirements.) At that point, smaller units—some portable and benchtop in size—can be utilized to deliver the water to the necessary purity level of individual labs or even individual researchers. Ideal for smaller laboratories without large quantity water needs, some benchtop units can even deliver Type I ultrapure water directly from tap water.
Of note when choosing a water system for your laboratory are the volumes and qualities of water your applications will necessitate. Other important considerations include filter costs, ease of use and available water storage and system space, if applicable.
* ASTM International (formerly the American Society for Testing and Materials)
** For more information on water types, refer to ASTM D1193-91.
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