Do Cheap TDS Meters Work?

By April Jones
Colorado based water researcher, hiker, and outdoor enthusiast.

I often get quite a few questions about TDS meters and TDS measurements.  While I love when people take steps to learn more about their water, some people have used TDS 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. 

What is TDS?  What Does A TDS 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.  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 rises.  This is why there's no such thing as deionized water in nature.  Depending on a region’s geology, natural TDS levels can vary across the US, 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 Meter Not Measure? Because TDS is an aggregate measure of charged compounds in water, uncharged things like motor oil, gasoline, many pharmaceuticals, and pesticides do not contribute to a TDS measurement.  For example, a glass of deionized water with Glyphosate (the herbicide known as RoundUp) dissolved into it at 100 times higher concentration than allowed by the EPA for drinking water will have a TDS reading of 000. 

What About Lead, Fluoride, Chlorine, Arsenic or Chromium 6? Even though these toxic metals & chemicals are charged when dissolved in water, a TDS meter does not give meaningful information about their presence or concentration in water.  There are two main reasons for this:  1) A TDS meter is a non-selective 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 magazine article was not the lead concentration, it was the water's natural TDS level (which is dominated by minerals like calcium, magnesium, and sodium). 

2) 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 yard stick to measure a child's weight. It's the wrong tool.  For example, we recently tested water in the lab that had Lead 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 meter (or any other handheld device).  They must be measured by trained staff in analytical laboratories that use much more sophisticated scientific equipment. 

Do Epic Water Filters Water Pitchers or Under the Sink Filter Lower TDS? No.  Epic's filters selectively filter harmful things from your water like Lead, Fluoride, Hormones, Chromium 6, Pesticides, Pharmaceuticals, Petroleum products, Bacteria (Nano Pitcher), Virus (Nano Pitcher), Cysts (Nano Pitcher) Disinfection byproducts, and things that make water taste and smell bad (Chlorine, Chloramine, Sulfur).  Epic's home water filtration products do not remove minerals like calcium and magnesium because there’s no reason to. 

Should I Buy a TDS Meter To Test My Water For High TDS Levels? No. There is absolutely no reason to drink low TDS 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 Meter? If you have a TDS meter, we recommend giving it to a school or a curious child who has an interest in science!  Use the 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 the results!   

Keep Learning The Truth About TDS 

Pay attention to the fine print in ZeroWater's advertisements. They do not claim to remove water contaminants or that 0 TDS water is healthy or free from contaminants.