You may have heard that TDS meters can help screen for contaminants in water, but are they an effective way to tell if water is safe to drink? While TDS meters (also known as TDS testers) are affordable, finding out what it measures and how it works is the first step to determining if getting a TDS meter to measure your water is worth your while. 

What does TDS mean? 

TDS stands for Total Dissolved Solids, and when it comes to water, TDS refers to the amount of total dissolved solids present in the tap water. “The problem with these “TDS readings” is that the meters don’t really measure Total Dissolved Solids. They measure the electrical conductivity of the water, and then infer the true-TDS.  These meters can only give you an estimate of the ionized impurities in the water, and some of those like calcium and magnesium are good for you.” LARQ Chief Technology Officer, Doug Collins PhD, explains, “To measure true-TDS, you need to evaporate the water from a sample and weigh the residue. ”

TDS meters do not even detect specific contaminants. TDS meters detect the inferred total dissolved solids based on conductivity, including minerals that may be good for you, that are present in the water — whether it’s lead or calcium. 

Where do TDS come from? 

TDS in drinking water can come from natural sources, sewage, industrial wastewater, urban run-offs, chemical fertilizers, and even chemicals from the water treatment process. Since water is a universal solvent, it can easily pick up matter along the way, absorb and dissolve these quickly. Hence, the term “dissolved solids”. 

How is TDS measured?

TDS is measured in the total organic and inorganic matter dissolved in water combined. It is expressed in milligrams per liter (mg/L) or parts per million (ppm) and includes anything present in the water that isn’t H2O. 

A TDS meter will detect any charged ions in the water, which could include positively charged ions such as calcium, sodium, magnesium, and potassium or negatively charged ions such as carbonate, hydrogen carbonate, chloride, sulfate, and nitrate. Salts and minerals that may appear in water are also ionized and thus can increase the conductivity of water—resulting in a higher TDS reading. Essentially, a TDS meter measures a solution’s electrical conductivity in order to estimate the TDS, not the specific contaminants, and it cannot determine if the water is a health hazard. 

Do TDS meters measure if water is safe to drink?

The answer is no. Many water filtration companies will tout their low or zero TDS meter ratings with their products, but this is not the best way to determine water quality overall because they can’t differentiate between ions—resulting in an unmeaningful measurement. In fact, TDS meters do not even detect pharmaceuticals, motor oil, arsenic, chromium-6, pesticides or even PFAS, which we know pose a great threat to our health in drinking water. 

TDS meters only measure ionized impurities, not electrically neutral ones. For example, lead in high-pH water is neutral so won’t show up on an electrical-TDS reading; large organics, like pesticides and pharmaceuticals, are almost always neutral. Thus, TDS meters won’t tell you if these toxic chemicals are present in the water. 

As we learned from a previous report on lead contamination in water, lead in any amount is dangerous to the human body, so even a trace amount should be treated seriously with effective filtration. Thus, in this sense, TDS meters fail to detect harmful contaminants or even distinguish between good and bad dissolved solids in water. 

How to read TDS measurements

Although there is no EPA limit for TDS, the EPA does recommend that TDS concentration should not exceed 500 mg/L or 500 ppm. This is considered a Secondary Drinking Water Standard since it is not deemed a health hazard, but may affect the taste and smell of the water. 

Here is a chart to help illustrate good or bad levels of TDS in water. : 

Take this chart with a grain of salt. 

All filters change the pH of water. That can change the ionization of impurities so it can look like filters add or reduce true-TDS when they really only change the conductivity of the water without adding or removing anything. In addition, some ionized impurities contribute to the water’s electrical conductivity more than others. So a high electrical-TDS reading could mean you have high true-TDS, or it could mean you have trace levels of a very conductive ion. Without expensive testing, it is not possible to understand what’s going on in the water. 

Alternatively, if you’re looking for something to measure the hardness of water, you can try water hardness test strips. These test trips only measure hardness in the sense of how many minerals (good or bad) are in the water, and not whether the water is safe to drink.  A high rating might indicate that there is a lot of sediment within the water that might cause limescale for instance—something that people making coffee or tea might want to know. Just note that water hardness test strips are not a means for determining overall water quality.

No matter what, it is still recommended to use a point-of-use filter such as a water filter pitcher to remove contaminants before preparing food as well as coffee or tea. 

Why do water filtration companies recommend using TDS meters to measure water quality?

You might be wondering why people use TDS meters if they are so unhelpful. Well, the simple answer is that TDS meters are easily accessible, and therefore, people may find it helpful to see some kind of difference when testing out a new product. Companies know that seeing results that are remotely scientific will increase sales, so by optimizing their water filtration to have a 0 ppm TDS reading, they can provide “proof” that their product works—even when it doesn’t tell the whole story. TDS meters are not considered the gold standard by any stretch, and they are not helpful for measuring water safety or contamination levels.

Then, how do we know if a water filter is effectively removing contaminants? 

1. Third-party testing and certifications help consumers find products that actually work for them. 
2. Look for third-party lab reports that provide individual results for a list of contaminants that includes those you are concerned about in your tap water. Additionally, look for testing against NSF standards, an ANSI-accredited standards system for determining if water treatment systems and components are reliable treatments for potable water. Typically, to pass NSF standards, the water treatment product must remove, at minimum, 90% of the contaminant in order to be deemed effective. (Note: This number could vary depending on the type of contaminant.)
   
   For any of our products, from the LARQ Bottle Filtered to the LARQ Pitcher PureVis, we provide third-party lab reports to show the efficacy of our technology with full transparency. As an added layer of protection, the LARQ Pitcher PureVis also has PureVis technology, which maintains the cleanliness of the water being filtered by eradicating bio-contaminants that tend to fester in wet environments such as these.
   
   We want our customers to be happy with their choice, so if you have any specific questions you can’t find in our testing, feel free to reach out to us at hello@livelarq.com.
   
3. The best way is always to do your own research of contaminants; we like to use the EWG tap water database to easily identify contaminants in our own municipal water supply. Then, cross-reference that list with the contaminant list or third-party lab report water filtration product that you are considering to ensure it’s the perfect solution for you.