By Jay Anand
Water analysis can be as easy or as involved as you want it to be. Often we may convince ourselves that the more difficult the water analysis, the more accurate the results. This isn’t always the case, however. With new test strip innovations, water analysis has become a task that can be performed by the average person while producing accurate, reliable results under most conditions and demands. The first step in trusting test strips is to become familiar with the answers to frequently asked questions (FAQs) about test strips. The following questions and answers are simple and to the point.
Question: How do test strips work?
Answer: Test strips are small strips, typically produced from plastic “sticks,” with chemically impregnated pads on the end. These pads are designed to react with specific ions and produce a specific color change. Once a test strip is reacted, and a color is developed, the strip is then compared to a printed color chart. The printed color chart is specifically designed to represent color reactions at various concentrations. Matching the strip to the closest color match produces a concentration reading. Currently, there are no agencies specifically setup to evaluate test strip performance. However, individual manufacturers can solicit independent reviews from several agencies such as the NSF International or the U.S. Environmental Protection Agency (USEPA).
Q: How accurate and reliable are test strips?
A: Test strips can be quite accurate. Most manufacturers utilize several industry-standard reference methods to compare and calibrate their strips. One of the most comprehensive collections of reference methods is contained in the American Water Works Association (AWWA) manual for water and wastewater treatment and evaluation. Once the standard reference method is established, the test strip manufacturer determines the level of accuracy that the strips should meet; generally, the accuracy is within a color block up to the expiration date of the strip. The test strip is put through multiple testing phases and scenarios to see how it performs in real-world situations. After the grueling testing phase, the data are collected and the results are evaluated. If the test strip meets the desired level of performance, it’s accepted and ready for distribution. Competent test strip manufacturers won’t release a test strip if its performance doesn’t meet the highest possible accuracy and reliability.
Q: Can I use a drinking water quality test strip in my pool or spa?
A: Generally, it’s recommended that you use a test strip that has been specifically designed to work in the water sample that’s being tested. Most test strips are designed to test either drinking water quality or pool and spa water quality. When an incorrect water sample is tested using a water quality test strip, the results can often still be acceptable. As an example, if a water quality free-chlorine test strip is used in pool water, the results will more than likely be correct to within a color block on a colormetric chart. The reason for this is that pool water and drinking water have similar chemical properties. Still, be sure that you’re using the right strip for your application to help avoid any inaccurate results.
Q: How accurate are the test strip color charts?
A: The color charts, supplied with test strips, are the most important factors in getting reliable results. The test strip can be the best available but if the strip pad colors don’t match the colors printed, then accuracy suffers. To provide the most accurate color charts available, manufacturers employ tried-and-true quality control procedures. Beginning with the design work and through the final printing of the color charts, the quality control staff monitors the process. Quality control members also do a 100 percent check of all printed labels before use. Before the test strips are shipped, the labels are checked once again to make sure the test strip lot and color chart label meet quality control specifications. By employing such a system, test strip manufacturers are able to provide accurate products.
Q: When I use the test strip, I get a color that isn’t on the supplied color chart. Why does this happen and what does this mean?
A: Occasionally, a user will get a color that isn’t on the chart. When this happens there are several possible explanations. First, the user needs to make sure the directions were followed closely. When manufacturers develop a test strip and write the directions, the times and procedures provided are written in detail for a reason. Oftentimes, a user didn’t follow directions closely, which may result in the strip developing an unusual color. Keep in mind that while most test strips look similar, the directions for the strips can be very different. This can be true even when dealing with test strips from the same manufacturer. Second, an unmatchable color can develop if the sample has a certain level that isn’t represented on the color chart. When a color chart is developed for a test strip, the manufacturer has to make a couple of choices—what are the common levels encountered in testing for this ion, and what’s the separation between the colors, i.e., how distinguishable are the colors from each other. Several different things can cause a color that doesn’t match what’s on the color chart. Commonly, it can mean that the level you’re detecting isn’t included on the color chart. Try to extrapolate the concentration of color for the best estimate. Sometimes when the color doesn’t match at all, this can be caused by interference ions in the sample. When this occurs, contact the manufacturer to see if another, more appropriate, test is available.
Q: Are test strips approved by the U.S. Environmental Protection Agency (USEPA)?
A: Most test strips aren’t USEPA approved; however, there are a few under USEPA evaluation and pending approval. One such strip measures free chlorine. This test strip measures as low as 0.05 parts per million (ppm) and has an accuracy of 97 percent, when compared to an AWWA free-chlorine method. Once this strip and others like it are approved, they may be used as reportable screening methods for testing drinking water. This can save time and money. In a home setting, this type of strip is affordable, offers professional quality results and provides consumer confidence.
Q: Which test strip brand should I use?
A: There are several test strip brands currently available on the market. When choosing the test strip company that’s right for you, ask yourself a few questions. First, how long has the company been manufacturing test strips? Experience can be a good indicator of expertise and knowledge in the market. Traditionally, the longer the manufacturer has been in business, the more reliable the test strips offered. Second, are test strips the only product that’s manufactured by the company? It’s best to go with a company whose major focus is test strips. Companies that produce a wide variety of products can often provide a test strip that isn’t as refined as possible. At the same time, companies that only produce test strips focus only on the products they offer. Although this isn’t the only indicator of quality, it’s a good place to start. Third, what brand are others in my field using and what is their opinion? Peer recommendations can be a great source of information because they have already been through the task of looking at all the fine details. A great source for this information is to visit the Water Quality Association’s website (www.wqa.org) and search for test strip manufacturers. Fourth, is price representative of the quality? The test strip market is very competitive. Manufacturers go out of their way to make sure the best product is being made available to you at a reasonable price.
Q: I am interested in purchasing test strips. Where should I begin?
A: Trade publications—whether for the pool & spa industry or point-of-use/point-of-entry water treatment industry—are often a great place to look for available test strips. Most test strip manufacturers advertise on a regular basis. Once you have composed a list of the manufacturers, contact each one and request some free samples. A test strip manufacturer that believes in their products will be more than happy to provide samples. And always make sure you evaluate these samples under typical use conditions.
When dealing with test strips, there are many different questions that can arise based on your particular situation and application. The above is provided to give you a place to start when making your decision. The best way to find the answers to your questions is to contact the manufacturer directly. After all, the best user is an educated user.
About the author
Jay M. Anand is the marketing manager for Industrial Test Systems Inc., of Rock Hill, S.C. Manufacturing test strips since 1989, Industrial Test Systems developed the first free chlorine test strip to be evaluated by the USEPA and the first user-friendly arsenic field kit that detects to 2 parts per billion (ppb). Anand can be reached at (803) 329-9712, (803) 329-9743 (fax) or email: email@example.com.