How To Measure TDS

The TDS Meter Explained

Sometimes with water filtration, a TDS meter will show no change to the TDS reading between tap water and water filtered by a water filter. There’s a common theme in response to this statement: Why?

Let’s Talk About TDS

First, it’s important to know what TDS really is: Total Dissolved Solids.  After water falls to the ground as rain, it dissolves the minerals present in the rocks and soil it passes over or through.  As it dissolves these minerals, they remain in the water at varying levels of concentration.  This is a very natural process and it helps make water taste “right” by slightly raising the pH of the water.  The most common minerals found in water are Calcium, Magnesium, and Sodium.

Some areas of the country have higher levels of these dissolved minerals in their water making it “hard” and other areas have lower levels.  Anything under 500 mg/L (or ppm) is good and 300 mg/L is considered excellent.  As the TDS level goes below this level (as the minerals are removed) the water has a lower pH and becomes more acidic or corrosive.  This causes a noticeable difference in the taste of the water.  TDS levels over 2000 mg/L are considered non-potable (don’t drink that stuff).

Measuring TDS

A TDS meter is a small hand-held device used to indicate the Total Dissolved Solids in a solution, usually water. Since dissolved ionized solids, such as salts and minerals, increase the conductivity of a solution, a TDS meter measures the conductivity of the solution and estimates the TDS from that reading.TDS Meter

Next, the question might arise, do I need a TDS meter? The short answer is: no. A TDS meter does not give any type of reading about what contaminants might be in the water, and while some dissolved solids are bad, many dissolved solids are beneficial. Getting water tested using a test kit will provide a report that explains exactly what’s in the water – including dissolved solids.

Keep in mind a water filter is not a water softener. The ultimate goal of water filter is not to remove all solids in the water. In order to know what’s in the water, skip the TDS meter and get the water tested for contaminants.

Then – Why Water Filtration?

One of the reasons Aquasana filtered water tastes so good is because we utilize a selective filtration process.  All of our drinking water filters use the same process and we call that the Aquasana Claryum® Filtration Technology. Our filter is certified to remove 77 contaminants including chlorine, chloramines, lead, pharmaceuticals, pesticides, herbicides, etc.  However, we specifically DO NOT remove the minerals in the water.  We filter out the bad but leave in the good – and some of what makes it good are those TDS’s.  The Claryum selective filtration process will make water taste more natural because we filter water back to the form nature intended.

The Aquasana Claryum Filtration Technology utilizes three main processes.  First, carbon absorption – this removes most of the organic compounds (chlorine, pharma, pesticides, herbicides, etc).  The body is mostly carbon, so this filtration process acts much like the human body would.  Our filtration process here is better than gravity pitchers because we use a dense carbon block and pressure instead of granulated carbon and gravity.  The result is much greater contact time of the water with the carbon even though the filtration process is faster.  Cool, huh? 

Second, mechanical filtration – this removes particles larger than 0.5 microns such as giardia or cryptosporidium (which are chlorine resistant parasites).  This kind of filtration doesn’t come from most gravity filtration products, either.  This only happens with extremely slow filtration or by utilizing pressure.  Last, ion exchange – this is how heavy metals like lead and mercury are filtered.  Basically, we have a potassium ion mixed with the carbon which is designed to grab any particles with a positive charge (i.e. heavy metals) and replace those particles with potassium.  This filtration process can actually result in a small increase in TDS concentration.

All that said, there are some dissolved solids that should not be in drinking water.  They are very rare in tap water, but things like arsenic can find its way into tap water at low levels of concentration.  The local water suppliers are required to do a water quality test and make the results public.  If there is arsenic in the water, it would show up on this report.  Additionally, fluoride is added to tap water in most cities in the US. If there is arsenic in the water or if fluoride removal is desired, reverse osmosis water filtration is the way to go.


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