Even scientists with decades of lab experience might know very little about measuring water quality. While most realize that lab procedures depend on water quality, assuming purity can be more common than measuring it. Many lab scientists might never even think of what should be measured.
If that sounds like you, read on. In this article, I will cover the importance of reagent-grade water as well as review available resources. Before you continue reading, however, I recommend checking out this primer on reagent-grade water.
First, let me describe a bit of my experience with lab water quality. It relied entirely on assumptions. If the device in a lab stated that it contained deionized water or doubly deionized water, that’s what I assumed it was. I never thought, not for one second, that I should confirm that water quality. In addition, if I had decided to test that water, I wouldn’t have had any idea what to test. I’d be the guy holding a beaker of lab water up to the light and saying, “Looks good to me!”
As it turns out, there’s more to it than that.
Obtaining an explanation … of sorts
As the primer mentioned above notes, water gets contaminated with many things: inorganic ions, lots of organic things—from microorganisms to humanmade things—and more. How much of that needs to be removed to make water reagent-grade depends on the intended use of the liquid.
After decades of ignoring water quality, I wanted guidance on what to measure and why. Surely, I thought, I can find something that would give me a better idea of what to measure, now that measuring something about water—besides maybe its freezing or boiling point—finally occurred to me.
Hoping for specific guidance about reagent-grade water, I turned to the U.S. National Institutes of Health, which reported: “Reagent grade water (RGW) is water that is suitable for use in a specified procedure such that it does not interfere with the specificity, accuracy, and precision of the procedure.”
That makes sense. RGW should not get in the way, more or less, of a process or procedure. Far enough, but that didn’t put me any closer to knowing what to measure or why.
Parameters to measure
If you want to test anything, it’s worth seeing what ASTM International thinks. Once known as the American Society for Testing and Materials, this seemed like a good place to look. It was, as soon as I found ASTM D1193, which is the organization’s “Standard Specification for Reagent Water.”
I recommend the 2018 version, because plenty of scientists who think about water quality more than I ever did gave the ASTM some things to think about in the prior reagent-water specification. That aside, even the abstract states: “This specification describes the required characteristics of reagent waters.” Just be prepared to discover that the sort of abstract and seemingly qualitative descriptions that some organizations use for reagent-grade water might seem a bit more user-friendly than ASTM’s approach.
The ASTM specification for reagent-grade water states: “Four types of waters have been specified, with three additional grades that can be applied to the four types.” The four general categories arise from the method of preparation: distillation, ion exchange, reverse osmosis, and so on—in various combinations plus some measurements. The latter include electrical conductivity and resistance, pH, total oxygen content, the concentrations of some ions, like sodium and chloride, microbes, and more.
It all sounds pretty definitive, until the part of the specification that states: “It is the responsibility of the users of this specification to ensure that the selected water types or grades are suitable for their intended use.”
To an extent, perhaps relying on the doubly-deionized water in a lab was not such a terrible choice.
Is water quality qualitative?
Making media for a cell-culture lab seems like the precise place that the water should meet certain requirements. Maybe there’s more control over the water quality in such applications than there was in my day, nearly 40 years ago. Back then, the entire process seemed a little relative. Consider that we used a collection of “products” called rat-tail collagen, chick-embryo extract, and horse serum—two of which we made in the lab. I’m guessing that the doubly deionized water didn’t add the highest variance to the process.
Another engineering-based perspective I reviewed was from Chemical Engineering, which offered some promise in an article title “High-Purity Water Simplified.” As it turns out, this source stuck to the standard conclusion: “There is no absolute single standard for water quality, and deciding whether water quality is suitable or not depends on circumstance and intended purpose.” This explanation did give a bit of hope when it noted that “there is general consensus on the parameters to be measured in order to evaluate water quality.” That hope faded fast as the article reminded readers that “it is important to keep in mind that the actual water quality varies greatly depending on the application that the researcher wishes to perform and the depth of the data that he or she aims to acquire.”
So, my beaker-holding, light-looking technique might not offer much value, but if that water came from a device that promises to provide some form of processed water, that might be the best that an everyday scientist can hope to accomplish in the world of using reagent-grade water. Water-quality experts might disagree, even adamantly. But here’s the thing: Lab life gives scientists plenty to worry about, and it’s the job of manufacturers to make sure that a water purifier does what it claims to do.