Volume 44 Number 2
Testing of Microbiological Water Treatment Devices
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While the six ANSI/NSF Drinking Water Treatment Unit (DWTU) Standards cover many point-of-use and point-of-entry (POU/POE) claims and technologies, there has been a noticeable gap with respect to microbiological treatment. Microbiological claims available today within the current standards include cysts (Standard 53), bacteriostasis (Standard 42), microbiological reduction by ultraviolet (UV) disinfection (Standard 55) and distillation (Standard 62). The obvious areas missing from this list include mechanical reduction of bacteria and viral contaminants, along with other disinfection technologies such as ozone and halogen.
The NSF Standards Department and DWTU Joint Committee are working collectively to develop new test methods and criteria for these additional technologies and claims. Once complete, these new standards will take the place of another widely recognized standard, EPA Standard and Protocol for Testing Microbiological Water Purifiers (EPA Guide Standard). The U.S. Environmental Protection Agency (USEPA) guideline has come to be the recognized method and criteria available today for testing of broad microbiological treatment claims beyond existing ANSI/NSF Standards.
The EPA Guide Standard
The EPA Guide Standard contains technology-specific test protocols for halogenated resins, UV treatment systems and ceramic candles. It provides the general framework to develop specific test protocols for any other technology. For example, this framework includes specifications for the challenge water characteristics designed to simulate a worse case untreated water source. It also includes provisions for elevated levels of turbidity, total dissolved solids (TDS), and total organic carbon (TOC), high and low pH conditions, and varying water temperatures, depending on the type of technology. Three separate tests are conducted according to the standard. A protozoan cyst reduction test can be completed according to either the EPA Guide Standard or ANSI/NSF Standard 53 using live cysts or microspheres. The bacterial reduction challenge is performed using Klebsiella terrigena, and a mixed challenge of Polio and Rotavirus are used for the viral challenge. Use of MS2 coliphage for the viral testing, though not specified in the EPA Guide Standard, has been accepted by the USEPA as a suitable alternative. Reduction requirements for all three tests are shown in Table 1.
ANSI/NSF Microbiological Treatment Standards status
An important point of agreement among the various committee members was to separate out claims for safe vs. unsafe water supplies. The draft definitions are as follows:
Safe water: Drinking water deemed acceptable for human consumption by an appropriate health or regulatory agency having jurisdiction.
Unsafe water: Water that 1) is known to contain disease-causing bacteria, viruses, protozoa or other disease-causing microbiological agents; 2) shows a positive test for an indicator organism; 3) is determined unsafe by an appropriate health or regulatory agency, or 4) hasn’t been shown to meet appropriate health agency microbiological guidelines.
Conversely, the treatment of safe water has been more controversial. Through much debate, the current, generally agreed upon position is to require bacterial and viral claims to be combined, while allowing reduction of cysts and heterotrophic plate count (HPC) bacteria to be separate claims. The draft criteria are provided in Table 3.
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