Laboratory Water Quality Standards

Technical standards on water quality have been established by a number of organizations including the American Society for Testing and Materials (ASTM), International Organization for Standardization (ISO), United States Pharmacopoeia (USP) and the Clinical and Laboratory Standards Institute (CLSI) - previously known as the US National Committee for Clinical Laboratory Standards (NCCLS). CLSI outlines Clinical Laboratory Reagent Water (CLRW) guidelines.

ASTM Standards for Laboratory Reagent Water (ASTM D1193-91)

ASTM: American Society for Testing and Materials

Measurement (Unit)Type IType IIType IIIType IV
Resistivity (MΩ-cm)> 18> 1> 4> 0.2 (200KΩ)
Conductivity (µS/cm)< 0.056< 1< 0.25< 5
pH at 25˚CN/AN/AN/A5.0 - 8.0
Total Organic Carbon  (TOC) ppb or µg/L< 50< 50< 200N/A
Sodium (ppb or µg/L)< 1< 5< 10< 50
Chloride (ppb or µg/L)< 1< 5< 10< 50
Silica (ppb or µg/L)< 3< 3< 500N/A

The ASTM standards are further subdivided into A, B and C that can be used in conjunction with the type I, II, III or IV water above when bacteria levels need to be controlled.

Additional ASTM Sub-Standards for Laboratory Reagent Water

Measurement (Unit)ABC
Heterotrophic Bacteria Count (CFU/ml)< 1< 10< 1000
Endotoxin (units per ml)< 0.03< 0.25N/A

ISO 3696 Standard

ISO: International Organization for Standardization

Parameter Grade 1 Grade 2 Grade 3
Conductivity µS/cm (temp corrected)< 0.1< 1< 5
pH at 25°CN/AN/A5.0 - 7.0
Oxidizable matter Oxygen (02) content mg/LN/A< 0.08< 0.4
Absorbance at 254 nm and 1 cm optical path length, absorbance units< 0.001< 0.01N/A
Residue after evaporation on heating at 110°C mg/kgN/A< 1< 2
Silica (Si02) mg/L< 0.01< 0.02< N/A

CLSI-CLRW Guidelines

CLSI-CLRW: Clinical and Laboratory Standards Institute - Clinical Laboratory Reagent Water
CLSI was formerly known as NCCLS (US National Committee for Clinical Laboratory Standards)

Contaminant Parameter and Unit Type 3 Type 2 Type 1 CLRW
IonsResistivity (MΩ-cm)> 0.05 (50 KΩ)> 1> 18> 10
OrganicsTotal Organic Carbon (TOC) ppb< 200< 50< 10< 500
Pyrogens(Eu/ML)N/AN/A< 0.03---
ParticlesParticles > 0.2 µm (units/mL)N/AN/A< 1 (0.22 µ  filtration  required)Include 0.22 µ filtration
ColloidsSilica (ppb)< 1000< 100< 10---
BacteriaBacteria (cfu/mL)< 1000< 100< 1< 10

These values are best used as guidelines, as many applications require further treatment based on other factors. For example, many molecular biology applications require Type 1 water that is free of DNase and RNase and simple washing of instruments (usually Type 3) might require water that is pyrogen free for critical applications (Type 1).

Laboratory Water Purity Specifications 'Consolidated' Guidelines

ContaminantParameter and UnitType 1Type 2Type 3
IonsResistivity (MΩ-cm)> 18> 1> 0.05 (50 KΩ)
 Silica (ppb)< 10< 100< 1000
OrganicsTotal Organic Carbon (TOC) ppb< 20< 50< 200
ParticlesParticles > 0.2 µm (#/ml)< 1N/AN/A
BacteriaParticles > 0.2 µm (#/ml)< 1< 100< 1000
 Endotoxin (Eu/ML)< 0.001N/AN/A

Typical uses for each type are outlined below:

Type 1Required for critical laboratory applications such as HPLC, Mobile Phase Preparation, blanks and sample dilution for analytical techniques such as GC, HPLC, AA, ICP-MS, etc. Preparation of buffers and media for mammalian cell culture and IVF. Production of reagents for molecular biology applications (DNA sequencing, PCR). Preparation of solutions for electrophoresis and blotting.
Type 2Used in buffers, pH solutions and microbiological culture media preparation and for preparation of reagents for chemical analysis. Used in clinical analyzers, cell culture incubators and weatherometers, etc. Also used as feed water to Type 1 systems.
Type 3Used for glassware rinsing, filling autoclaves and heating baths and humidifiers. Also used as feed water to Type 1 systems.


USP Standards

USP: United States Pharmacopoeia

PropertiesUSP 'Purified Water'USP 'Water for Injection' & 'Highly Purified Water'
Conductivity (µS/cm @ 25°C)< 1.3< 1.3
Total Organic Carbon (TOC) ppb or µg/L< 500*< 500*
Bacteria (guideline)< 100 cfu/ml< 10 cfu/100ml
Endotoxin (EU/ml)N/A0.25 EU/ml

*Or pass oxidisable substance test 

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