ASTM D1193 Explained: Choosing the Right Reagent Water Type
Reagent water is the silent ingredient in almost every analysis. Here is how ASTM D1193's four purity levels map to real lab work.
If you run an analytical lab, reagent water is everywhere — in blanks, in dilutions, in mobile phases, in final rinses. And yet it is easy to treat as a commodity. ASTM D1193 is the standard that reminds us it is anything but: the purity of the water you use directly determines whether your results are trustworthy.
Four types, four purposes
ASTM D1193 defines four purity levels, each tied to measurable parameters — chiefly electrical resistivity and total organic carbon (TOC):
- Type I — the highest purity (≥ 18 MΩ·cm, TOC ≤ 50 ppb). Used for the most sensitive work: trace metal analysis, HPLC, gas chromatography.
- Type II — general laboratory use, reagent preparation, and qualitative analysis (1.0 MΩ·cm, TOC ≤ 50 ppb).
- Type III — routine analyses, glassware washing, and rinsing (4.0 MΩ·cm, TOC ≤ 200 ppb).
- Type IV — general use where lower purity is acceptable (0.2 MΩ·cm).
Why the type matters to your data
Using a lower grade than your method requires is a classic source of false positives — trace contaminants in the water show up in your blank and get attributed to the sample. Using a higher grade than necessary is not dangerous, but it is expensive. Matching the water type to the method is one of the simplest ways to protect data integrity.
How IAS fits in
We run ASTM standardized testing across the Type I–IV spectrum as part of our scheduled QA programs, and we help facilities confirm that the water feeding their instruments actually meets the grade their methods assume. If you are unsure which type your workflow needs, that is exactly the kind of conversation we like to have.