Hydro, Inc.

Water Purification Specialists

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Water Quality Standards

There are multiple professional organizations that establish specific standards according to their fields of study. The most common of these organizations are:

  • Clinical & Laboratory Standards Institute (CLSI); formerly known as the National Committee for Clinical Laboratory Standards (NCCLS)
  • College of American Pathologists (CAP) (follows CLSI standards)
  • American Society for Testing & Materials (ASTM)
  • United States Pharmacopeia (USP)

American Society for Testing and Materials (ASTM)


Standard Specification for Reagent Grade Water
Type IType IIType IIIType Iv
Electrical Conductivity Max (pX/cm @ 25C)0.0561.00.255.0
Electrical Resistivity Min (MOhms-cm @ 25C)181.04.00.2
pH @ 25&#176C---5.0-8.0
TOC max (µg/L)10050200No Limit
Sodium max (µg/L)151050
Silica max. (µg/L)33500No Limit
Chloride max (µg/L)151050
When bacterial levels need to be controlled, reagent grade types should be further discussed as follows:
Type AType BType C
Total Bacterial Count Max CFU/100ml1101000
Endotoxin max. IU.ml0.030.025-

Clinical and Laboratory Standards Institute (CLSI) (CAP)
CLRWType IType IIType III
BacteriaBacteria (CFU/ml)<10<1<100<1000
Pyrogens(Eu/ML)-<0.03n/an/a
IonsResistivity (MΩ-cm @ 25C)>10>18>1>0.05 K50Ω
ColloidsSilica (ppb)-<10<100<1000
ParticlesParticles >0.2 µm (units/mL)Include 0.22 µ filtration<1 (0.22 µ filtration required)n/an/a
OrganicsTotal Organic Carbon ppb<500<10<50<200

United States Pharmacopoeia Standards (USP)
Purified WaterWFI Water
Electrical Conductivity Max (µS/cm @ 25C)<1.3<1.3
Total Organic Carbon (TOC) (ppm)<0.5*<0.5*
Endotoxin (EU/ml)n/a<0.25
Bacteria (guideline only)<100 cfu/ml<10 cfu/100ml
* Or pass oxidisable substance test
When bacterial levels need to be controlled, reagent grade types should be further discussed as follows:
Type AType BType C
Total Bacterial Count Max CFU/100ml1101000
Endotoxin max IU.ml0.030.25-