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Sistemi per il trattamento dell'acqua
      water system treatment

Quality standard

Purified water is commonly used in many industries and scientific organizations, for analytical purposes or in production processes. Therefore in order to encourage a better use, some international organizations have established quality standards for each type of application into:

  • ISO (the International Organisation for Standardisation )
  • ASTM (the American Society for Testing and Materials)
  • NCCLS (the National Committee for Clinical Laboratory Sandards)
  • the Farmacopoeia

These quality standards have led to the definition of three degrees of purity:


Water essentially used for the dissolution of ionic and organic pollutants colloids. It is also used in high-precision analysis, in particular in HPLC chromatography. This type of water can be obtained starting from a GRADE 2 or through a further treatment with ion exchange resins, as well as a filtration on a porous septum to 0.2 microns for the elimination of organic residues possibly present, or for re-distillation.


Water characterized by a really very low concentration of both organic and ionic contaminants that colloidal, is typically used for precision analysis, including atomic absorption spectrometry and in the determination of trace elements. This type of water can be obtained for multiple distillation or by treatment with reverse osmosis followed by ion exchange resins


indicated water for general purposes of the chemical laboratory and in solution of the reagents preparations. This type of water can be obtained by distillation, ion exchange or reverse osmosis.


Specifications of International Organisation for Standardisation
For laboratory water, it refers to ISO 3696: 1987

Parameter Grade 1 Grade 2 Grade 3
 pH - value at 25°C N/A N/A   5-7.5
 Electric Conducibility specifications at 25°C (microS/cm) 0,1   5
 Total Oxidable Carbon   O2 (mg/lt)  N/A 0,08   0,4
 Absorbance unit max. a 250 nm  0,001  0,01  NOT SPEC.
 Fixed residue fisso at 110°C (mg/lt)  N/A  1 2
 Silica max (mg/lt)  0,01  0,02  NOT SPEC.


Specifications of the American Society for Testing and Materials
Standard of reference for REAGENT GRADE WATER

Parameter Type I*
Type II**
Type III***
Type IV
 pH - value at 25°C - -  - 5-8
 Electric Conducibility specifications at 25°C (microS/cm) 0,056 0,1  0,25 5
 Electric Resistivity specifications (MOhm.cm) 18 10 4 0,2
 TOC (microg/lt)  100 150  200 no lim.
 Sodium max (microg/lt) 1 5 10 50
 Chlorides max (microg/lt) 1 5 10 50
 Silica max (mocrog/lt) 3 3  500 no lim.
*     request membrane filtration 0.2 microns        
**   water prepared by distillation        
*** request membrane filtration 0.45 microns        


Where there are to be carried out microbiological tests, followed by a further classification

Parameter Type A
Type B Type C
 Total bacteria max (UFC/100ml) 1 10  1000
 Endotoxins max (IU/ml) 0,03 0,25  -


Specifications of the National Committee for Clinical Laboratory Sandards (1988)

Parameter Type I
Type II
Type III
 Bacteria (UFC/100ml) <10 <1000 N/A
 pH - value at 25°C N/A N/A 5-8
Electric Resistivity specifications (MOhm.cm) >10 >1 >0,1
 Silica max (mg/lt) < 0,05 0,1 < 1
 TDS max (mg/lt) 0,1 1 5
 Total Carbon oxidable from O2 (mg/lt) < 0,05 < 0,2 < 1


Specifications of Farmacopea Europea e USF
Requirements of purified water for injection into body

Parameter EP
NITRATES < 0,2 ppm -
HEAVY METALS < 0,1 ppm -
TOC < 500 mg/lt C < 500 mg/lt C
BACTERIA < 100 UFC/ml < 100 UFC/ml


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