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 May 2007

Water, Water Everywhere

WATER, WATER EVERYWHERE, BUT IS IT PURE ENOUGH FOR LABORATORY WORK? For over 50 years, laboratories around the world have used ASTM standard D 1193, Specification for Reagent Water, to assure the proper purity of water used for analysis.

“When you think about doing analytical chemistry, whether you’re analyzing steel or oil or doing environmental monitoring, the most commonly used chemical reagent is water,” says John Hubbling, laboratory manager, Metropolitan Council Environmental Services, St. Paul, Minn. Hubbling has been chair of Subcommittee D19.02 on General Specifications, Technical Resources, and Statistical Methods since 2002, and co-chair with Verity Smith of the D 1193 task group since 2000. “We may not think of water as a reagent, but it is. You have to make up solutions in something. You have to dissolve your sample in something,” says Hubbling.

D 1193 was first approved in 1951 and, as stated in its scope, the specification “describes the required characteristics of waters deemed suitable for use with the standards under the jurisdiction of ASTM.” Four types of water are specified in D 1193, called Types I-IV. In addition, three separate grades that specifically address contaminants of microbiological origin can be applied to the four types. Laboratories use D 1193 to identify the kind of water purity level that is needed for their analytical application and then produce it as required by the standard.

Hubbling says that if water isn’t pure enough, or if it contains contaminants at sufficiently high levels, these contaminants will interfere with the lab work being done, either because they will cause distortion in the analytical process or because, if the water contains the chemical that the lab is trying to measure, it could appear that something is there when it’s not.

“It’s critically important to understand both how to purify the water and what the purity of the water is that you’re using to make sure that the reagent water being used will work for your particular application,” says Hubbling, who also notes that this is particularly important in the field of microbiology, since contaminants in water can affect the growth of bacteria that a laboratory may be trying to grow or count.

According to Hubbling, these issues have become increasingly important in the environmental field, especially over the last 40 years, since there has been a steady decrease in the levels where labs need to make their measurements. “We can now identify the impact of pollutants at much lower levels and so need to measure at these levels. The reagent water needs to be pure enough so that we don’t get false positive results in our tests,” says Hubbling.

During the period from 2000-2005, Subcommittee D19.02 worked on a major revision of D 1193 that was approved in 2006. This revision reflects many of the changes that have occurred in water purification over the last few decades. Acknowledging the wide variety of technologies that are now available, the standard now states that the types of water may be produced with alternate technologies as long as the appropriate constituent specifications are met and that the water so produced has been shown to be appropriate for the application where the use of such water is specified.

“D 1193 is ubiquitous, just as water is everywhere,” says Hubbling. “It is also unusual in that it must somehow incorporate the means of manufacture into a fixed specification while still trying to accommodate technological changes in the field of water purification.”

Hubbling believes that D 1193 holds a unique place in the world of ASTM standardization and he also believes that ASTM’s standards developing process is a vital component in the continuing success of the standard. “It might be the most widely cited ASTM standard; many people speak of “Type I” water not having any idea where the designation originates,” says Hubbling.

“D 1193 has set the standard for water specification for over 50 years. Once such specifications obtain such wide usage, it is ever more difficult to make changes and critical that updates are most carefully considered. The consensus process in ASTM, both in its inclusiveness and rigorousness, is vital to the success of maintaining the health of standards such as D 1193.”

Verity Smith agrees, noting, “D 1193 has certainly changed to keep up with technology and the needs of its users over the years.”