Water quality standards

For various fields of use and requirements.

International Organization for Standardization (ISO)

ISO 3696:1987 distinguishes between three degrees of purity for water for analytical purposes in laboratories.

ParameterGrade 1Grade 2Grade 3
pH value at 25°C 5.0-7.0
Conductivity (µS/cm at 25 °C)
Oxidizable matter,
oxygen content (mg/l, max.)
Absorption at 254 nm
and a lenght of 1 cm
(absorption units, max.)
Residue after evaporation by heating to 110 °C (mg/kg, max.) 12
Silicon content (mg/l, max.) 0.010.02

Clinical Laboratory Standards Institute (CLSI)

This institute defined the quality requirements of water for clinical laboratories. The regulations that were valid up to 2006 (NCCL types 1, 2 and 3) but were then invalidated by the requirement that water must be suitable for the intended usage. Only the degree of purity of so-called “Clinical laboratory reagent water” (CLRW) is described.

Resistance10 MΩ x cm
TOC< 500 ppb
Bacteria< 10 CFU/ml
Particle ContentInline 0.2 µm-filter

American Society for Testing and Materials (ASTM)

The ASTM D1193-06 (2011) deals with the requirements for chemical analyses and physical tests.



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