Water Quality InformationWritten By Actual ExpertsRSS
Eric Roy, PhD & Analies Dyjak, M.A.The Red Dye Test is a visual demonstration used in marketing materials by various water filtration companies. In this demonstration, red food coloring is added to water and passed through a filter, where it comes out clear. Oftentimes this demonstration is done in a “side by side” manner against another water filter that does not remove the red coloring from the water. This demonstration suggests to the consumer that:
If a water filter can remove red dye, it’s also removing dangerous contaminants. In scientific terms, they’re suggesting that red dye is a “proxy” or “surrogate” for dangerous contaminants.
Water filters that do not remove the red color are not as effective as water filters that do remove red food coloring.
Is Red Food Coloring a Representative Proxy or Surrogate for Contaminants in Drinking Water?
Absolutely not. Identifying a representative proxy/surrogate requires that a credible testing body (e.g NSF/ANSI) has actually done experiments to validate it. An example of a representative surrogate test is NSF/ANSI Standard 53 for VOCs, where the certifying bodies have shown (through testing) that chloroform is an effective surrogate for roughly 50 VOCs. No such testing has been done (or to our knowledge attempted) for red food coloring. It goes without saying, if the visual removal of red food coloring was a representative surrogate for water filter performance, credible water filter companies would not be spending millions of dollars on research, development, testing, and evaluation.
Are Water Filters That Do Not Remove Red Food Coloring Less Effective At Removing Dangerous Chemicals?
Absolutely not. For example, one of the brands that prominently markets using the red dye test was part of a water filter evaluation study conducted by Duke and NC State University, and failed miserably. Conversely, various products that do not remove red food coloring (Hydroviv’s included) were effective in filtering “hard-to-filter” PFAS from the challenge solutions. So while the brand effectively removes food-safe red dye, it isn’t able to remove PFAS. In fact, higher levels of PFAS were detected in the filtered water because the filtration media was likely oversaturated. In short, red dye is extremely easy to remove and is not an actual indication of filter performance or contaminant removal.
Is There a Quick and Easy Way To See if My Filter is Working?
While we wish there was an at-home test that could determine if your filter is doing its job, that unfortunately isn’t the case. Every home in America would test their water on a regular basis if at-home test kits provided actual information about water quality. If you want to test for contaminants, you’ll need to send a water sample to an accredited laboratory and test for a range of contaminants. This can cost thousands of dollars and doesn’t provide immediate results. The best way to ensure that you’re using an effective product is to buy products from companies that use third party testing & certifications.
Summary: The Red Dye Test is a Marketing Gimmick
The red dye test tells us almost nothing about filtration performance and shouldn’t be used as a proxy/surrogate for harmful contaminants.Other Articles Recommended For You:
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Eric Roy, Ph.D, | Scientific Founder
***Updated on March 22, 2022***
We get quite a few questions about TDS/ppm meters and TDS measurements. While we love when people take steps to learn more about their water, some people (including journalists from reputable publications - Example #1 and Example #2) have used TDS/ppm meters to draw false conclusions about water quality, which incited fear in people already in the midst of a terrible water quality crisis. In this article, we answer the questions that we get asked the most about TDS measurements and TDS meters. If you're curious about water filters that address meaningful contaminants, check out this recent water filter study by Duke/NC State.
What is TDS? What Does a TDS/ppm Meter Measure?
TDS stands for Total Dissolved Solids which is related to the total charged mineral content of water. TDS can be easily determined by measuring the conductivity of a water sample, which is exactly what inexpensive TDS probes do. TDS meters typically display the total amount of dissolved solids in parts per million of ppm. If you start with deionized water (which has a TDS of zero), and expose it to minerals that contain sodium, calcium, and magnesium... the water's TDS of ppm rises. This is why there's no such thing as deionized water in nature. Depending on a region's geology, natural TDS/ppm levels can vary across the U.S., and this variability has nothing to do with the water quality (except in extreme cases when the water is too salty to drink).
What Does a TDS/ppm Meter NOT Measure?
Because TDS/ppm is an aggregate measure of charged compounds in water, uncharged things like motor oil, gasoline, pharmaceuticals, and pesticides do not contribute to a TDS/ppm measurement. Most relevant to current nationwide water quality problems, TDS/ppm meters do not detect PFAS in drinking water. For example, the glass on the left in the picture above contains deionized water with Malathion (an organophosphate pesticide) dissolved into it at 100 times high concentration than allowed by the EPA for drinking water, and the TDS/ppm probe reads 000.Even though these toxic metals are charged when dissolved in water, a TDS/ppm meter does not give meaningful information about their presence or concentration in water. There are two main reasons for this:
A TDS/ppm meter is a nonselective measurement and cannot differentiate among different ions. A more sophisticated piece of equipment is needed to perform those types of measurements. The value of 184 that was measured using a TDS meter in a prominent Huffington Post Article was not the lead concentration... it was the water's natural TDS level (which is dominated by minerals like calcium, magnesium, and sodium).
A TDS tester is not sensitive enough to measure toxic levels of lead, chromium 6, or arsenic, even if they are present in a sample. This is because the reading displayed on an inexpensive TDS meter is in parts per million, while things like lead, chromium 6, and arsenic are toxic at part per billion concentrations (1000 times lower). Using a TDS meter to measure ppb lead concentrations in tap water is like trying to use a car's odometer to measure a child's height... it's the wrong tool for the job. For example, the water sample shown on the right hand side of this article's header image has levels that are 100x the EPA limit, and the TDS reading teetered between 000 and 001.
To reiterate: meaningful lead and arsenic measurements cannot be made using a TDS/ppm meter (or any other handheld device). They must be measured by trained staff in analytical laboratories that use much more sophisticated scientific equipment. Hydroviv Undersink filters are NSF/ANSI 53 certified to remove lead from drinking water.
Do Hydroviv Filters Lower TDS/ppm?
No. Hydroviv's filters selectively filter harmful things from your water (like lead, chromium 6, pesticides, pharmaceuticals, petroleum products, and disinfection byproducts), and things that make water taste and smell bad (chlorine, chloramines, and sulfur). Hydroviv's home water filtration systems don't remove minerals like calcium and magnesium because there's no reason to. In fact, we use some types of filtration media that actually add minerals to the water, so TDS/ppm levels in water filtered through a Hydroviv systems are sometimes slightly higher than unfiltered water.
Should I Buy a TDS/ppm Meter To Test My Drinking Water For High TDS Levels?
No. There is absolutely no reason to drink low TDS/ppm or deionized water. If you are concerned about water quality, put the money toward the purchase of an effective drinking water filter that removes harmful contaminants from your water.
What If I Already Have a TDS/ppm Meter?
If you have a TDS/ppm meter, we recommend giving it to a curious child who has an interest in science! Use it as an opportunity to teach them about dissolved minerals by encouraging them to test different types of water (e.g. distilled, rain, river, lake) and try to explain their findings! Feel free to reach out to use at firstname.lastname@example.org for educational ideals involving TDS meters.Other Articles Recommended For You:
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