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The Truth About TDS Meters And TDS Measurements

The Truth About TDS Meters And TDS Measurements

Eric Roy, Ph.D.  |  Scientific Founder

We get quite a few questions about TDS 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  Example #2) 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, the glass on the left in this article's header image contains deionized water with Malathion (an organophosphate pesticide) dissolved into it at 100 times higher concentration than allowed by the EPA for drinking water, and the TDS probe reads 000.

What About Lead, Arsenic or Chromium 6?

Even though these toxic metals 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:  

  • A TDS 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 an inexpensive TDS meter in a prominent Huffington Post Article was not the lead concentration… it was the TDS level (which is dominated by minerals like calcium, magnesium, and sodium) of the tap water.
  • A TDS meter 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 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 growth spurt…. It's the wrong tool.  For example, the water sample shown on the right hand side of this article's header image has lead concentrations 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 Hydroviv Filters Lower TDS?

No.  Hydroviv’s filters selectively filter harmful things from your water (like lead, chromium-6, pesticides, pharmaceuticals, petroleum products, disinfection byproducts), and things that make water taste and smell bad (chlorine, chloramine, sulfur).  Hydroviv’s water filters 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 levels in water filtered through a Hydroviv system are sometimes slightly higher than unfiltered water.

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 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 their findings!   Feel free to reach out to us at (info@hydroviv.com for educational ideas involving TDS meters). 

If you mail it to us, we’ll make sure it finds a good home in a school classroom, and we’ll send you a $20 coupon code to use on Hydroviv's website.

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