Understanding Total Dissolved Solids (TDS)

December 14, 2023 4 min read

Understanding Total Dissolved Solids (TDS)

Total dissolved solids, more commonly known as TDS, are a common point of misunderstanding in the world of water filtration. Total dissolved solids refer to the “total dissolved substances in water” (1). It includes minerals, salts, metals, and contaminants found in water. However, water containing a high concentration of TDS generally gets an undeserved bad reputation. Contrary to popular belief, waterdoes not need to have a low TDS to be considered “healthy.” In the following article, we will explain why. 

Testing TDS

Before delving into the ins and outs of understanding TDS, it is important to understand how TDS is measured. TDS can be tested by a tool called a TDS meter. When placed in water, this meter sends out an electrical current and measures the current’s resistance. The resistance of the current varies based on the amount of dissolved solids in the water (2). Based on the resistance, the TDS meter gives a numerical TDS level. 

A higher TDS level indicates more dissolved solids in the water. However, a TDS meter gives no indication of what these solids are. These solids are often trace minerals. Therefore, reading a TDS meter alone cannot determine if a water is healthy or not, as the meter cannot detect if the solids are healthy minerals or harmful contaminants. Another fallback of using a TDS meter is that, according to the Water Research Center, “the test does not provide us insight into the specific water quality issues such as hardness, salty taste, odors, corrosiveness, or the presence of trace metals” (3). While a TDS meter does its job to identify solids present in water, it cannot be used as a guide to understanding water quality. 

Is TDS important?

The impact of TDS is more aesthetic than anything else. However, the EPA still suggests that drinking water stays below 500 milligrams per liter, which is a fairly high threshold compared to the average TDS of tap water in the U.S. (4). As a “secondary contaminant,” TDS is not considered to hold risk of harmful health defects. Water’s TDS by itself does not give enough information to understand whether or not the water is harmful (1). 

Studies conducted on TDS conclude that more than anything, the TDS affects the taste of water (5). While water with a high TDS due to healthy minerals can come across as more flavorful, oftentimes water with an extremely low TDS is perceived as flat. For example, water filtered through a reverse osmosis filter has a TDS of nearly 0 milligrams per liter, but many complain of its taste being too flat for their liking (1). 

Common TDS Misconceptions

Myth: All dissolved solids are bad.

As previously mentioned, water with a higher TDS tends to get a bad rap. This is because many people believe any sort of dissolved solid found in their water is bad for them. Many solids are harmful if they are found in water, like heavy metals and other contaminants. However, there are also many solids that can help the body–namely, minerals. Healthy minerals like magnesium, calcium, potassium, and iron are also measured in a water’s TDS reading. These minerals actually benefit the body, and are credited to increasing hydration and boosting metabolism. 

Myth: TDS measures water quality.

Another common misconception about TDS is that it measures water quality, but this is not the case. The TDS simply shows you how many dissolved solids are found in water, but it does not specify if these solids are harmful or beneficial. Having a higher TDS does not make your water a health hazard (3). 

Myth: The lower the TDS, the healthier the water. 

Some types of water, like reverse osmosis water, boast their extremely low TDS reading. Nearly every solid is removed from these types of water, making it the most pure water. However, having a low TDS does not mean it is the healthiest. Alkaline water has a higher TDS than reverse osmosis water, but this is because healthy minerals are added to the water. These minerals increase the water’s TDS, but they also increase the health benefits of the water. 

TDS and Alkaline Water

Alkaline water is water that goes through a process called alkalization, where its pH is raised due to healthy minerals being added to the water. Alkaline minerals include calcium, magnesium, sodium, and potassium, and these minerals affect the body in many positive ways, like reducing acid reflux and balancing the body’s pH levels. Because these minerals are not filtered out of the water, alkaline water tends to have a higher TDS reading than other types of water. That being said, alkaline water is considered to be one of the healthiest types of water, as it is jam-packed with minerals beneficial to the body. 

The Wrap-Up

Total dissolved solids are commonly misperceived as a way to measure water quality. However, TDS simply identifies that solids are present in the water, but it cannot classify what these solids are. In some cases, like alkaline water, the TDS is elevated because of the presence of trace minerals. These minerals are purposefully added to the water to create a type of water healthier for the consumer. Therefore, TDS alone is not an accurate measure of water quality, but it is a good indication of solids found within water. To boost your water’s TDS in a healthy way, consider investing in an alkaline water filter. These filters accurately and efficiently filter out any harmful solids from your water, while leaving in any healthy alkaline minerals. 

Frequently Asked Questions

What do total dissolved solids indicate?

A water’s TDS indicates how many dissolved solids are present in the water. These solids can be minerals, salts, metals, cations, or anions.

How much TDS is safe for drinking water?

The Environmental Protection Agency suggests that the TDS of water should be under 500mg/L.

Is high TDS water harmful?

TDS alone is not an accurate measure of water quality. A high TDS could indicate a high number of harmful metals found in your water, but it could also indicate a high amount of healthy minerals. It is important to understand what is in your water, not just what the TDS meter indicates. 


  1. Safe Drinking Water Foundation,https://www.safewater.org/fact-sheets-1/2017/1/23/tds-and-ph 
  2. The Truth about TDS Meters and What They Actually Measure,https://www.youtube.com/watch?v=yHvdYWXiVzI 
  3. Know Your H20 Water Research Center,https://www.knowyourh2o.com/indoor-6/total-dissolved-solids#:~:text=An%20elevated%20total%20dissolved%20solids,rather%20than%20a%20health%20hazard
  4. W. Adam Sigler and Jim Bauder, Montana State University,https://waterquality.montana.edu/well-ed/interpreting_results/images-files/Alkalinity_pH_TDS.pdf 
World Health Organization,https://cdn.who.int/media/docs/default-source/wash-documents/wash-chemicals/tds.pdf?sfvrsn=3e6d651e_4