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Anna is a senior science editor at Technology Networks. She holds a first-class honors degree in biological sciences from the University of East Anglia. Before joining Technology Networks she helped organize scientific conferences.
From routine cleaning tasks to sensitive analytical applications, water is a fundamental resource used in the laboratory. However, water purity can have a significant impact on experiments and their accuracy, making it crucial to select water with the appropriate level of purity for the application it will be used for.
Download this infographic to explore:
Why water purity is important
How water purity is defined
Water purification processes
From routine cleaning tasks to sensitive analytical applications, water is a
fundamental resource used in the laboratory. However, water purity can have a
significant impact on experiments and their accuracy, making it crucial to select
water with the appropriate level of purity for the application it will be used for.
This infographic provides an overview of the types of laboratory water, their
suitability for different applications and methods of purification.
Several applications depend on high-purity water free from contaminants, and using the wrong
type of water can result in a range of issues with experiment accuracy and reliability, as well as
instrument safety and performance, including:
However, water purification can be expensive, and using higher-purity water than is needed can incur
unnecessary costs. It is, therefore, crucial to understand the type of water your application needs.
• Damage to HPLC pump and injectors
• Skewed results due to additional impurities,
particularly for trace analysis
• Interference with microbial growth
• Blockages in optical sensors and fluid lines
• Production of higher background values
• Contamination of cell culture
• Calibration sample errors
• Altered pH of testing solutions
THE IMPORTANCE
OF WATER PURITY
Despite being safe to drink, tap water
can contain low levels of impurities and
contaminants, such as suspended particles,
ions and dissolved gases, all of which can
impact experimental processes and results.
TYPES OF
LABORATORY
WATER
Three principal types of laboratory water
were defined by the 1998 National Committee
for Clinical Laboratory Standards Guidelines
for Classification of Water Types. Although
laboratory water is still commonly referred to
according to these types, alternate classification
systems have since been developed.
DEFINING WATER
PURITY
Several parameters can be used to define water
purity, including pH, conductivity and silica
content. The exact criteria used vary between
standards-setting organizations.
PURIFICATION
PROCESSES
Laboratory water can be purified using
a range of methods; the type of water
needed dictates the processes and
technologies used. The state of feedwater
used should also be considered.
MICROORGANISMS AND
MICROBIAL BY-PRODUCTS
including bacteria, viruses
and endotoxins.
DISSOLVED GASES
mainly oxygen, nitrogen
and carbon dioxide, with
traces of inert gases.
INORGANIC IONS
including sodium,
magnesium, calcium,
iron, chloride, sulphate
and nitrate.
ORGANIC
COMPOUNDS
wide variety of
compounds including
lignin and humic acid.
PARTICULATES
can be hard, soft or
colloidal.
• Purest form of water
produced.
• Produced using UV
light and ultrafilters.
• Easily contaminated
and must be properly
stored.
• Used in highly
sensitive applications
and analytical
procedures, including
chromatography, flow
cytometry, molecular
biology applications,
atomic absorption
spectroscopy and cell
and tissue culture.
TYPE I
ULTRAPURE
WATER
TYPE II
GENERAL
LABORATORY
GRADE WATER
TYPE III
PRIMARY
GRADE WATER
• High purity level.
• Produced using
reverse osmosis and
deionization.
• Used in applications
including media
preparation,
microbiological culture,
biochemical assays
and as feed water for
washing machines and
autoclaves or for Type I
production.
• Lower purity level.
• Produced using carbon
filtration and reverse
osmosis technology.
• Used in non-critical
basic lab applications
such as glassware
washing and as feed for
autoclaves or for Type 1
production.
• Cost-effective way to
reduce contaminants.
ASTM D1193-06 from ASTM International provides specifications for four types of reagent water,
based on pH, conductivity, resistivity, total organic carbon (TOC), and sodium, silica and chloride
content. Type I is the purest. Three sub-standards measure bacteria and endotoxins.
Conductivity – how well the water can conduct electrical current. Ion levels
and inorganic impurities are measured. Common measurement for raw
water and drinking water. Indicates the level of ions in the water.
Resistivity – how much the water resists conducting electrical flow.
Indicates the water’s ionic content.
TOC – indicates the presence of organic impurities. Oxidation products
are measured. Often used for Type I water.
pH at 298 K (25 o
C) — — — 5.0 to 8.0
TOC, max, µg/l 50 50 200 No limit
Sodium, max, µg/l 1 5 10 50
Chlorides, max, µg/l 1 5 10 50
Total silica,
max, µg/L 3 3 500 No limit
Type I Type II Type III Type IV
0.056 1.0
Electrical
conductivity,
max, µS/cm at 298
K (25 oC)
0.25 5.0
18.0 1.0
Electrical
resistivity, max,
MΩ-cm at 298 K
(25 oC)
4.0 0.2
ISO 3696:1987 from the International Organization for Standardization provides specifications for
three grades of water for analytical laboratory use based on pH, conductivity, oxidizable matter
oxygen content, absorbance, residue post-evaporation and silica content. Grade 1 is the purest.
The Clinical and Laboratory Standards Institute primarily focuses on a single standard for water for
clinical laboratories – Clinical Laboratory Reagent Water.
DISTILLATION
• Water is boiled and evaporated into steam.
• Impurities such as bacteria, organic
compounds and heavy metals are
removed.
REVERSE OSMOSIS
• Water is pushed through a semi-permeable
reverse osmosis membrane under high
pressure.
• A range of impurities, including ions and
organic compounds, are trapped and
removed.
• Pre-treatment is recommended to protect
the membrane.
ABSORPTION
• Activated carbon is used to remove
chlorine and chloramines.
• Chlorine is reduced to chloride and carbon
dioxide.
• Chloramines are broken down into
ammonia, nitrogen and chloride.
ULTRAFILTRATION
• Small pores eliminate contaminants,
including endotoxins, pyrogens, enzymes
and colloids.
• Prone to clogging.
ION EXCHANGE
• Water passes through beds of ionexchange beads.
• Ions such as magnesium, calcium and
chloride are removed and replaced
with hydrogen and hydroxyl ions, which
combine to produce water.
• Very effective at reducing ionic
contamination.
ELECTRODEIONIZATION
• Combination of electro-dialysis and ion
exchange technology.
• Ions are removed.
• Less prone to microbial contamination than
ion exchange resin beds.
ULTRAVIOLET OXIDATION
• Water flows through a UV chamber.
• Organic compounds are oxidized and
removed downstream by ion exchange.
• Microbial growth is also stopped.
NaCl H₂O
H+
OH⁻
Water purity can have a significant impact on experiments and equipment,
so it is important to consider the purification technologies needed to
produce the type of water suitable for your application.
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