Reagent Water

Preparation and Testing of Reagent Water in the Clinical Laboratory

In June of 2006 the Clinical Laboratory Standards Institute published the final draft of the 4th edition of “Preparation and Testing of Reagent Water in the Clinical Laboratory.” This is an international nonprofit standards-developing and educational organization that was previously known as NCCLS. Previous editions used Type I, II and III designations to differentiate quality of water in the lab. These designations have been replaced with more meaningful specifications and additional requirements.

Reagent Water

Reagent water is the most widely used analytical solvent in a clinical laboratory. The primary goal of every laboratory is to produce accurate results. In one manuscript it was estimated that 70% to 80% of HPLC performance problems were attributable to the quality of water used to prepare eluents, standards and samples. This is but one example of potential suitability issues covering water quality.

Goals of the 4th Edition

The 4th Edition recommends measuring certain parameters of purified water as a means of quality control. Those parameters are resistivity as a measure of ionic contamination; total organic carbon (TOC) as a measure of organic contamination; and viable plate counts as an indicator of microorganism contamination.

Regulated Environment

Operating in the current rigorous environment underscores the importance of validating that a given water is fit for its intended purpose. There are additional guidelines for system validation, ongoing maintenance and revalidation. A schedule for maintenance and meter veracity should withstand a laboratory audit.

Silica and pH

Previous measurements for pH and silica have not been carried forward but system design would be critical for weakly ionized contaminants (silica being one example). CO2 absorption by purified water and the subsequent drop in pH is a well-known phenomenon.

Basic Specifications

Basic specifications for CLRW would be 10 cfu/ml for bacterial contamination, resistivity of 10 megohm @ 25C as dispensed, a final filter of a minimum of .22 microns and organic impurities at less than 500 ppb. Addressing TOC contamination mimics the United States Pharmacopoeia minimum standard and is an excellent indicator of suitability for certain laboratory testing. The TOC may be measured remotely through testing. The test procedure is critical and it is difficult to maintain validation without in-house online testing.

Six types of Reagent Water are specified

  • Clinical laboratory reagent water (CLRW)
  • Special reagent water (SRW)
  • Instrument feed water
  • Water supplied by a method manufacturer
  • Autoclave and wash water
  • Commercially bottled, purified water

All must begin with potable water.

Water Suitability

Suitability of particular water for an application must be determined. Special reagent water standards would need to be determined for such applications as trace organic analysis, DNA and RNA testing, trace metals analysis, cell/tissue/organ culture and fluorescent antibody detection of microorganisms. You may also need to address endotoxin, sterility or CO2 content.

Materials of construction

The standard addresses materials of construction and materials of laboratory equipment. It must be considered that borosilicate chemical resistant glass will contribute to trace amounts of ions in purified water and that some flexible tubing can add significant TOC to purified water.

Air quality

Not overtly addressed in the 4th Edition are air quality and its effect on purified water. As a general rule, if it is in the air it is in the water. CO2 absorption is well known but any volatile organic liquid or even agar production will taint highly purified water.

New Direction

The roughly 70 pages of the 4th Edition take clinical laboratory water in a new direction. The reality of validation and suitability are emphasized throughout. It is no longer a matter of meeting a water quality but being able to demonstrate that the water quality promulgated is being met, that it will continue to be met and that it is suitable for the task at hand.

About Total Water Treatment Systems, Inc.

Total Water Treatment Systems a leading supplier of high purity water to dialysis clinics, biotech companies, laboratories, manufacturing and food processing plants in Wisconsin, Minnesota, Illinois and Iowa. Learn more at or by calling 1-800-929-2236.

Request an In-Depth Quote

Call 608-220-2883 to speak to a representative immediately or fill in the form and we’ll contact you within 1 business day!

* Required