Reagent grade water is actually a broad term applied to water purified for laboratory uses. It has been defined at three or four distinct purity levels or types by professional societies concerned with the quality, uniformity and reproducibility of tests or materials requiring purified water. The precise definitions of each water type, however, vary from society to society. So your specific reagent grade water needs will depend primarily on the intended use of the water, using specifications offered by the society most applicable to your situation as a guideline.

In the clinical laboratory field, the College of American Pathologists (CAP) and the National Committee for Clinical Laboratory Standards (NCCLS) have published or proposed standards for reagent grade water. For other laboratories, the American Society for Testing and Materials (ASTM) and the American Chemical Society (ACS) have established standards. A summary of specifications for each grade of water is contained in the Reagent Grade Water Specification Table.

In general, Type I water is used for procedures requiring maximum accuracy and precision such as HPLC, atomic absorption spectrometry, flame photometry, enzymology, blood gas, pH, and specific ion determinations, reference buffer solutions, and the reconstitution of lyophilized materials used as standards. Type II is designated for most analytical and general laboratory testing and hematological, serological and microbiological procedures. Type III is suitable for most qualitative analyses, urinalysis, parasitology and histological procedures, the making of stock solutions, and rinsing of laboratory glassware.

Reagent Grade Water in CAP Accreditation
The College of American Pathologists, beyond its definitions of reagent grade water, has also included in its accreditation checklist certain mandatory and recommended procedures concerning laboratory purity water. For example, laboratories seeking CAP accreditation must have a system in use, with written procedures, for checking purity of water. A permanent record of purity checks, to verify conformation to reagent grade specifications, must be maintained. Specifically recommended checks are resistivity, pH, hardness, sodium, ammonia, and cultures.

Exton makes no representation that these standards are suitable for your needs.


Type I Type IIA Type IIB Type III Special*

Trace elements

Ligand assay


Microbiology systems (not to be sterilized)

Stains & dyes (histology/parasitology)

Microbiology systems (to be sterilized)

Bacteriological media preparation


Chromosome analysis HLA testing w/ ultrafilter

For selected purposes, additional requirements beyond those specified for Type I water may not be necessary. This chart lists several of these selected purposes.

View the standards of water purity, which features guidelines from the National Committee for Clinical Laboratory Standards (NCCLS), the College of American Pathologists (CAP), and the American Society for Testing Materials (ASTM).


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