• Editorial – A New Water Standard
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Water is the most widely used laboratory chemical and, as a solvent, it is likely to be used in concentrated form. What then are the implications for science and technology when the most widely referenced consensus standards for laboratory water are woefully inadequate? Clearly, the implications are very great and laboratories would be well advised to scrutinize standards on which the reliability of their applications depend, especially when a flaw in such a standard could result in errors that would not be readily apparent. Laboratories must never lose sight of the fact that the consensus process is theoretically democratic, not scientific! And, in reality, it is rough and tumble politics, especially when profits are at stake.¹ Only in this context is it possible to understand:

• How standards that require no validation, overflow with inconsistency and error, and defy interpretation could come to be accepted by manufacturers of water purification systems and regulatory agencies.
  
  
• Why many laboratories are so focused on achieving a resistivity of 18 megohms-cm that they loose all sight of organic and microbial contaminants –which are the real villains for most bioscientific and medical applications and are not detected with resistivity testing–;² and
  
  
• Why laboratories believe that relatively low cost resistivity meters, which cannot be cleaned or calibrated and may be fixed to prevent them from displaying impossibly high values,³ would be sufficiently accurate to distinguish between water with a resistivity of 18 megohms-cm –the minimum limit of ASTM Type-I water– and water with a resistivity of 17 megohms-cm.

Based on the premise that laboratory water standards should derive their validity from scientific reason and widespread voluntary approval, not from authoritarian fiat, scientists have developed a new standard. The AH/LabWater-1, Standard for Laboratory Reagent-Grade Water, uses a matrix of process and product parameters to permit the orderly specification of reagent-grade waters. The approach provides anyone with a need to communicate, document, or specify the quality of reagent-grade laboratory water with the option to select the specification that best suits the requirements for a given application. And the approach permits the extension of specifications in future versions of the Standard without altering existing specifications. The AH/LabWater Standard is informative and practical. Extensive application notes provide guidance for the use of the specifications; however, the notes will also be immensely helpful to anyone responsible for operating or purchasing water purification equipment. Laboratories will find the new standard useful for improving water quality, documenting methods, preparing protocols, and selecting systems. A free copy can be downloaded from the Lab Water Standards tab at the High-Q Web site (select the Ad Hoc menu button on the left of the screen).

¹ Refer to the Lab Water Standards tab of the High-Q Web site for a complete discussion of laboratory water standards.

² The organic and microbial contaminants present in water that has been treated with ion exchange can be killed and removed with ozone, UV, ultrafiltration, distillation, etc., but these steps can reduce the resistivity of the water somewhat. Refer to the Lab Water References tab of the High-Q Web site for additional articles.

³ Resistivity meter cells are almost always installed at the point in a system where the highest readings are obtained, rather than after all stages of purification, which, unless this fact is disclosed, can amount to fixing the meter. Also, as cell electrodes become coated (insulated) with biofilm, uncorrected readings should rise above what would be theoretically possible; however, meters may be fixed, so they will not display high values that would tip the user off to improper calibration. If it is possible to feel, or wipe, a film off any accessible internal surfaces of a purification system, it is very likely that the resistivity cell electrodes are also coated. And if a cell cannot be removed for cleaning , it may not be possible to use effective cleaning agents (i.e., a mixture of ethyl ether, isopropyl alcohol, and dilute HCl) without damaging the components of the rest of the water purification system. Resistivity meters that can be calibrated to +/- 0.5% at 18 megohm-cm over a practical temperature range are likely to cost several thousand dollars. It is important to bear in mind that the observed resistivity of pure water will change by about 3.5 to 5% for every 1° C change in the temperature of the water (between 20° and 30° C).