ASTM D1193 (Types I–IV)
| 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 |
*Requires use of 0.2 μm membrane filter; **Prepared by distillation; ***Requires the use of 0.45 μm membrane filter.
Clinical and Laboratory Standards Institute (CLSI) – formerly NCCLS
As of 2006, the CLSI has moved away from the typical Type I, II and III designations, instead preferring to suggest that water be simply ‘fit for purpose’, and only describes one grade in significant detail: Clinical Reagent Laboratory Water. The CLSI has also briefly outlined other grades in less detail, such Special Reagent Water (SRW) and instrument feed water.
| Parameter | CLSI-CLRW |
| Resistivity (MΩ·cm at 25°C) | ≥10.0 |
| Conductivity (µS/cm at 25°C) | ≤0.1 |
| TOC (ppb) | ≤500 |
| Bacteria (CFU/mL) | ≤10 |
| Endotoxins (EU/mL) | ≤0.25 |
| Silica (mg/L) | ≤0.05 |
| Particulates | 0.22 µm filtration recommended |
| pH | Not specified |
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 |
| Resistivity (MΩ·cm at 25°C) | ≥10 | ≥1 | Not specified |
| Conductivity (µS/cm at 25°C) | ≤0.1 | ≤1.0 | ≤5.0 |
| TOC (ppb) | ≤50 | ≤50 | Not specified |
| Bacteria (CFU/mL) | ≤10 | ≤100 | Not specified |
| Silica (mg/L) | ≤0.01 | ≤0.02 | ≤0.05 |
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