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Reagent Water
Quality
Introduction
Water quality is an important consider-
ation in the laboratory because it can
significantly affect the outcome of
laboratory procedures and the measure-
ment of patient samples.
This bulletin provides an overview of
reagent water quality guidelines as
specified by the National Committee
for Clinical Laboratory Standards
(NCCLS).
1
Use these guidelines to
evaluate the reagent water quality in
your laboratory and to determine the
best method for obtaining the water
quality you need.
Good laboratory practices suggest that
you establish a protocol that supports
the manufacturer’s requirements for the
instrument to:
• ensure optimum performance of
automated laboratory instruments
• eliminate water quality as a source of
problems when troubleshooting
• help you to meet requirements for
state and federal laboratory
certification
What is Reagent Water?
Reagent water is laboratory water that
meets specifications for clinical
laboratory use.
2,3
The NCCLS has defined three grades
of reagent water:
• Type I, the highest grade
• Type II, the intermediate grade
• Type III, the lowest grade
Technical
Bulletin
from Bayer Business Group Diagnostics.
Table 1 lists the NCCLS specifications for the three types of reagent water. Use
this information to determine the water quality in your laboratory. Refer to the
NCCLS guidelines for common laboratory uses of Type I, Type II, and Type III
reagent water.
Table 1. Reagent Water Specifications
Specification Type I Type II Type III
Maximum bacterial content 10 (preferably bacteria 1000 not applicable
colony forming units per free)
mL (CFU/mL) *
pH not applicable not applicable 5.0 – 8.0
Minimum resistivity 10 (inline measurement 1.0 0.1
(megohm/centimeter at by sensor or resistor)
25°C) †
Maximum silicate (mg/L) ‡ 0.05 0.1 1.0
Particulate matter (µm) § smaller than 0.22 µm not applicable not applicable
(water is passed through
a 0.22 µm filter)
Organic compounds ** pretreat with activated not applicable not applicable
carbon
* Bacterial content: The number of colony forming units in water. Bacterial content is a water contam-
inant you measure to determine water quality.
† Resistivity: The ability of water to resist electrical conduction due to the ion content. Resistivity is the
standard test measurement for determining water quality. The higher the resistivity, the lower the ion
content and the better the water quality.
‡ Silicates: Compounds you remove to produce Type I reagent water.
§ Particulate matter: Undissolved (insoluble) substances larger than 0.22 µm are removed by the filter.
** Organic compounds: Compounds you remove to produce Type I reagent water.
Purifying Water
As with all diagnostic testing procedures, good laboratory practices suggest that
you establish a protocol that supports the manufacturer’s requirements for
selecting the appropriate type of reagent water. You can then produce reagent
water in your laboratory by setting up and maintaining a water purification system
which uses the purification methods described in Table 2.
Table 2 describes some of the typical laboratory water purification methods.
Table 2. Water Purification Methods
Method Description
Distillation Changes water from liquid to vapor and leaves behind
impurities such as particulates and bacteria
Deionization Uses synthetic resins to remove ionized impurities by ion exchange
Reverse Osmosis Forces water under pressure through a semipermeable membrane
to remove dissolved solids and organic impurities
Adsorption Uses activated carbon, clays, silicates or metal oxides to remove
organic impurities
Filtration Forces water through a semipermeable membrane to remove
insoluble matter, emulsified solids, pyrogens, and microorganisms