| Contaminant | Parameter and unit | Type 3 | Type 2 | Type 1 |
| Ions | Resistivity (MΩ•cm @ 25°C) | >0.05 | >1.0 | >18.0 |
| Organics | TOC (ppb) | <200 | <50 | <10 |
| Pyrogens | (EU/mL) | NA | NA | <0.03 |
| Particulates | Particulates > 0.2 µm (units/mL) | NA | NA | <1 |
| Colloids | Silica (ppb) | <1000 | <10 | <10 |
| Bacteria | Bacteria (cfu/mL) | <1000 | <100 | <1 |
International Organization for Standardization (ISO)
The ISO based its specification on ISO 3696:1987, and specifies three grades of water: Grade 1, Grade 2 and Grade 3, where Grade 1 is the most pure (see below):
Water quality parameters for ISO grades
| Parameter | Grade 1 | Grade 2 | Grade 3 |
| pH value at 25oC | – | – | 5.0–7.0 |
| Conductivity (μS/cm) at 25oC, max | 0.1 | 1.0 | 5.0 |
| Oxidisable matter Oxygen content (mg/l), max | – | 0.08 | 0.4 |
| Absorbance at 254 nm and 1 cm optical path length, absorbance units, max. | 0.001 | 0.01 | – |
| Residue after evaporation on heating at 110oC (mg/kg), max | – | 1 | 2 |
| Silica (SiO2) content (mg/l), max | 0.01 | 0.02 | – |
American Society for Testing and Materials (ASTM)
The ASTM uses D1193-06 and has four grades of water (see table below).
Water quality parameters for ASTM types
| Parameter | Type I* | Type II** | Type III*** | Type IV |
| Conductivity (μS/cm) at 25oC, max | 0.056 | 1.0 | 0.25 | 5.0 |
| Resistivity (MΩ-cm) at 25oC, max | 18.0 | 1.0 | 4.0 | 0.2 |
| pH at 25oC | – | – | – | 5.0–8.0 |
| TOC (μg/l), max | 50 | 50 | 200 | No limit |
| Sodium (μg/l), max | 1 | 5 | 10 | 50 |
| Silica (μg/l), max | 3 | 3 | 500 | No limit |
| Chloride (μg/l), max | 1 | 5 | 10 | 50 |