By Rick Andrew
Disinfection of water to prevent disease can be accomplished with a variety of technologies and approaches and is one of the primary focuses of those in the water industry. As such, various NSF/ANSI standards related to water address disinfection technology through detailed and rigorous testing requirements. Some have wondered why there are multiple standards and test methods related to disinfection efficacy. After all, disinfection is disinfection and water is water, right?
Unfortunately, the world of water treatment is rarely as simple as anyone would like it to be. And the case of disinfection is certainly one of these. If we look at disinfection of recreational water versus disinfection of drinking water, we can see some fundamental differences of application and requirements that drive the need for different testing methods.
Recreational versus drinking water
Water is water, but the end use of water for recreational purposes is significantly different from that of drinking water. These differences manifest themselves in the various considerations related to treatment and ultimately how to test and evaluate treatment systems. Let’s consider the following:
Water quality. Drinking water typically has low levels of disinfection chemicals. In cases where the source is surface water, it can also have low TOC concentrations (a few parts per million) in the form of natural organic matter. This matter is derived from decaying leaves and other material in surface waters and is broken down by natural decay and also water treatment. Recreational water, on the other hand, has potentially higher levels of disinfection chemicals and also may have higher levels of organic carbon due to the presence of sunscreen products, oils and other organic contamination related to people swimming in the water.
While it is important for drinking water treatment manufacturers and practitioners to remember that drinking water derived from a surface water source may contain some TOC, the organic contamination of recreational water creates a much more significant consideration for its treatment. It is important that the water quality used for testing disinfection and treatment efficacy reflects the water being treated, especially when it comes to organic contamination that can be present in recreational water. This means using potential fouling contaminants (such as baby oil) when preparing test water for testing treatment efficacy of recreational water disinfection systems. These organic contaminants can potentially interfere with treatment by causing fouling, reducing UV transmissivity or increasing chemical disinfectant demand. As such, it is very important in terms of meaningful test requirements to be sure they are represented in the water used for testing.
Exposure. Exposure to contaminants that may be present in drinking water is primarily through ingestion. Exposure to contaminants in recreational water, however, involves skin contact, potential inhalation of volatilized chemicals (including disinfectants) and potential limited ingestion. These differences in exposure lead to differences in treatment requirements and acceptable concentrations of contaminants that may be present in the water. In most cases, considerations related to ingestion are more significant, leading to lower acceptable residual contaminant levels and more stringent treatment criteria related to drinking water treatment. Nonetheless, it is important to remember the differences in applicable exposure pathways with drinking water and recreational water.
Single-pass versus multiple-pass treatment. Drinking water is treated one time by POU/POE systems as it passes through and then is consumed or used in some way. Recreational water, on the other hand, is repeatedly pumped and cycled through the pool and treatment systems, leading to multiple-pass-type treatment. It is important to consider these differences when evaluating efficacy of disinfection and treatment through equipment testing. Just as it would be inappropriate to include multiple passes when testing POU/POE drinking water treatment systems, it would not be fair to require complete treatment of recreational water in a single pass. The multi-pass nature of recreational water treatment allows for a more economical approach to equipment design and operation, which must be considered when developing testing standards and methods.
Flow control and inlet pressure
The pressure associated with drinking water supplies can vary quite a bit depending on whether the supply is pumped from a private well or delivered by a public water supply. Public water supply pressure can vary throughout the distribution system based on elevation and other factors. These variations in supply pressure lead to challenges for POU/POE equipment suppliers who are counting on specific flowrates for adequate disinfection and treatment to be provided. Recreational water is recirculated by pumps in a very controlled way, with both pressure and flowrate being designed and controlled within the system itself. This makes it much easier to manage application of treatment technologies within a recreational water system as compared to a drinking water system.
Once again, it is very important that these differences be reflected in the standards and requirements. For example, when testing POU/POE UV drinking water disinfection under NSF/ANSI 55, the equipment is tested at the highest achievable flowrate, measured at pressures up to 120 psi, with the result being that UV treatment systems conforming to NSF/ANSI 55 include flow restrictors to prevent excess flowrates that would hinder treatment efficacy. For recreational water, it is not as important to include this type of flow restriction requirement in the standard because in the field, flowrates through the equipment can be much more easily engineered, constructed and ultimately, controlled.
Water is water?
Many things that at first seem simple reveal themselves to be much more complicated after a superficial first look. This is certainly true of water treatment. The uninitiated may be tempted to think that ‘water is water’ and ‘one size fits all’ when it comes to water disinfection and treatment systems. As we can see in this analysis of the differences between drinking water and recreational water end uses, it is certainly the case that the design, construction and evaluation of treatment equipment intended for drinking water treatment is significantly different from that of equipment intended for treatment of recreational water. And this is just one example—there are many others. Consider treatment of boiler, cooling tower and ship ballast water, seawater and many more. Each is different from drinking water or recreational water and from the other examples listed. Indeed, it is not difficult to conclude that water is not just water.
About the author
Rick Andrew is NSF’s Director of Global Business Development–Water Systems. Previously, he served as General Manager of NSF’s Drinking Water Treatment Units (POU/POE), ERS (Protocols) and Biosafety Cabinetry Programs. Andrew has a Bachelor’s Degree in chemistry and an MBA from the University of Michigan. He can be reached at (800) NSF-MARK or email: [email protected]