Berkey Filters and TDS Meters


Many of our customers have written in asking why their new TDS meter does not register much of a change between their pre-filtered water and the post-filtered water.  This is actually normal, and the answer has to do with what a TDS meter actually measures.  According to, “Total Dissolved Solids (TDS) are the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water, expressed in units of mg per unit volume of water (mg/L), also referred to as parts per million (ppm). TDS is directly related to the purity of water and the quality of water purification systems and affects everything that consumes, lives in, or uses water, whether organic or inorganic, whether for better or for worse.”

What a TDS meter reading or a PPM count actually means

The above statement from the TDS meter website is both correct and incorrect.  It is correct in what a TDS measurement consists of, namely the “total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water”.  It is incorrect in its conclusion that TDS is related to the purity of the water and the quality of the water purification system.  If the measure of a water purification system was how close it could make water to pure H2O, then maybe it would be correct.  But, people need minerals to live.  Thus, helpful minerals in your water are actually a good thing.  Thus, you can and should have a quality water purification system that filters out things that are harmful to your body, but leaves in the helpful things such as minerals.

So, when our customers use a TDS meter, what they often find is that the reading both before and after the water has gone through the Black Berkey purifiers is about the same.  And they are correct.  The Black Berkeys do NOT take out the beneficial minerals.  Thus, of the things that a TDS meter will actually detect, the Black Berkey purifiers will only remove the unwanted heavy metals such as lead and mercury as well as sedimentary minerals such as iron oxide and aluminum.  Therefore, your TDS reading will not change much unless you have a significant amount of heavy metals or sedimentary minerals in your water.

Does this mean a high TDS reading is inherently good? No! But at the same time, it also doesn’t mean a high TDS count is inherently bad. It just depends on what those solids are. The important thing is to not simply rely on a TDS meter for your measure of whether your water is good. You can have low TDS count water that has harmful bacteria in it. You can have high TDS count water that is perfectly safe (e.g. – pure, un-polluted ocean saltwater…albeit, you wouldn’t drink it, but that’s only because the mineral is salt). Thus, make sure you know what your TDS meter is actually telling you.

Posted in Water.

One Comment

  1. I’ve purchased a Big Berkey with Flouride filters. The taste is superior to what is was before with chlorine and Flouride. The smell of chlorine is very strong in our tap water. I am concerned that we may have a high level of flouride in our water and need to change filters early of the 6 months. I have Hyperthyroidism and a Goiter so it is essential that I remove Flouride from my life. Please recommend a quality flouride test strip so that I can tell when Flouride is getting through. I’ve done some research with little results and need to find the cheapest that still provides quality test results. Thank you.

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