International Organization for Standardization (ISO)
ISO 3696:1987 distinguishes between three degrees of purity for water for analytical purposes in laboratories.
pH value at 25°C | – | – | 5.0 up to 7.0 |
Conductivity at 25 °C [µS/cm] | 0.1 | 1.0 | 5.0 |
Oxidizable matter, oxygen content [mg/l, max.] | – | 0.08 | 0.4 |
Absorption at 254 nm and a lenght of 1 cm (absorption units, max.) | 0.001 | 0.01 | – |
Residue after evaporation by heating to 110 °C (mg/kg, max.) | – | 1 | 2 |
Silicon content [mg/l, max.] | 0.01 | 0.02 | – |