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Water in the Laboratory - A Tutorial

Overview of Lab Water Grades

Norms define different laboratory water grades for both technical and economical reasons. The purpose of these norms is to ensure that the right water quality is used for a specific application, while limiting laboratory operating costs – Type 1 water is more expensive to produce than Type 2 or Type 3 water.

Type 3Type 3 water is the lowest laboratory water grade, recommended for glassware rinsing, heating baths and filling autoclaves, or to feed Type 1 lab water systems.

Type 2Type 2 water is the grade used in general laboratory applications such as buffers, pH solutions and microbiological culture media preparation; as feed to Type 1 water systems, clinical analyzers, cell culture incubators and weatherometers; and for preparation of reagents for chemical analysis or synthesis.

Type 1Type 1 water is the grade required for critical laboratory applications such as HPLC mobile phase preparation, blanks and sample dilution in GC, HPLC, AA, ICP-MS and other advanced analytical techniques; preparation of buffers and culture media for mammalian cell culture and IVF; production of reagents for molecular biology applications (DNA sequencing, PCR); and preparation of solutions for electrophoresis and blotting.

Using Type 1 water for Type 2 water applications is a common laboratory practice in order to decrease the risk of artifact generation during experimental procedures.

Laboratory Water Specifications
Different published norms define the quality required for specific laboratory water applications: ASTM® and ISO® 3696 for laboratory applications; CLSI guidelines for clinical laboratories. Some laboratories will also use norms defined in the European or the US Pharmacopoeia.

The table below outlines the different water specifications based on the different water types:

ContaminantParameter and unit
Type 3
Type 2
Type 1
IonsResistivity (MΩ•cm @ 25°C)
OrganicsTOC (ppb)
ParticulatesParticulates > 0.2 µm (units/mL)
ColloidsSilica (ppb)
BacteriaBacteria (cfu/mL)

These values are only guidelines, as some specific laboratory applications may require a quality superior to the quality indicated by the norms. For instance, several molecular biology applications require Type 1 water that is both RNase-free and DNase-free; elemental trace analysis at sub ppt levels requires water of a higher purity than regular Type 1 water; and glassware washing may require pyrogen-free water for some experiments. Millipore has done extensive research into laboratory water applications. This information, compiled as internal research notes or references to scientific articles, is provided on demand by our Application Specialists. (Visit www.millipore.com/offices to find your nearest contact).

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