What is a TDS meter and do you need one?

If you’re concerned about the quality of your tap water but are unsure if you need a water filter, you may have heard about using a TDS meter (also known as a TDS tester) to check for contaminants. A TDS meter is generally easy to use and relatively affordable with some starting as low as $10. However, before buying one you should know that it does not, in fact, check for the presence of contaminants in water. 

Learn about TDS including what a TDS meter is, what it measures (and doesn’t), and other helpful information to determine if you actually need one.



First, it’s important to know what TDS really is: Total Dissolved Solids. TDS in water refers to the amount of total dissolved solids in your tap water. 

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. According to the Water Quality Association, water in the 120 mg/L (or ppm) and above range is considered hard, with 180 mg/L being considered very hard. Water in the 80 to 100 mg/L range is ideal, meaning it’s not too hard and has the right amount of dissolved minerals for optimal taste. As the TDS level goes below 17 mg/L, (as the minerals are removed) it becomes “soft”, with a lower pH and more acidity.  

In addition to inorganic materials like minerals, TDS also features a small amount of organic material from sources such as leaves, sewage, and waste as well.

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 meters may be referred to as TDS testers or PPM (parts per million) testers, but all of these are different names for the same thing. TDS meters can be purchased for as low as $10, but more advanced models can cost $1,000+ based on the level of accuracy and additional features offered.

For example, a basic TDS meter may only measure the amount of total dissolved solids in a solution while an advanced model may be able to check salinity, temperature, and more. 



 A high TDS level means you have an abundance of dissolved solids in your water, which typically includes minerals. Over time, the constant presence of these minerals in your water can lead to scale buildup in your pipes and appliances which shortens their lifespan and effectiveness. By knowing your TDS level, you can determine whether you need something to combat this issue, like a Salt-Free Water Conditioner or a water softener for, especially hard water. 

Salt-Free Water Conditioners inhibit scale buildup by transforming dissolved hard minerals into harmless, microscopic crystals that don’t accumulate over time. Salt-Free Water Conditioners can protect pipes and plumbing, decrease spots and stains on dishes and shower doors, increase the life of brighter clothing, and more, without wasting salt or water. Keep in mind that a Salt-Free Water Conditioner is different from a water filter. The ultimate goal of a water filter is not to remove all solids in the water.

What does TDS not measure?

A TDS meter does not measure contaminants. It will not tell you if your water is healthy. The TDS meter reading simply refers to the amount of total dissolved solids in your water, it will not tell you what those solids actually are and if they are harmful for your health.  

For example, you could have a high TDS meter reading but no harmful contaminants in your water. Some healthy minerals like potassium, magnesium, and calcium can actually cause your TDS meter to spike. So, any water filter with a remineralizer could cause a high reading on your TDS meter, even though the remineralizer is adding good minerals that you want. 

On the other hand, you could have a low TDS level even if several harmful contaminants are present in your drinking water. Your water could have heavy metals like lead, or other contaminants like pesticides, pharmaceuticals, or hexavalent chromium. The TDS meter will not pick these contaminants up. 

This is why you shouldn’t rely on a TDS meter to determine your water quality. You need to understand not just how many dissolved solids are in your water, but what those solids are and if they’re harmful for your health.