Total Dissolved Solids: What is TDS and How Does it Work?

Total Dissolved Solids: What is TDS and How Does it Work?

The First Step in Getting to Know Your Water

If you’re in the market for a water filtration system, or if you’ve ever carefully read the label on a bottle of water, you may have seen the term “TDS”. But what is TDS? What is “good” TDS? And how is it calculated? Below, we take a deep dive into the definition, nuances, and significance of TDS.

What is TDS and how does it work

How TDS works

TDS stands for “total dissolved solids”. H2O is a really excellent solvent, meaning that it can easily hold onto impurities that dissolve within it. Those impurities then make up a small percentage of the solution that we call “water”, a complex substance that is often far more than just molecules made from hydrogen and oxygen. TDS measures just how many of those extra, dissolved substances can be found within water.

Dissolved solids fall mainly into four different categories: minerals, salts, dissolved metals, and other organic matter. Minerals such as magnesium, calcium, and potassium come from natural sources and can often be found in mineral waters and spring waters. While salts can be found in groundwater, they are equally as likely to come from manmade sources like deicing compounds, fertilizers, water softeners, and sewage contamination. Metals can be stripped from water pipes, come from mining or industrial waste, or be found naturally in rocks or soil. Finally, organic matter occurs when algae and plant material decompose. If you drink water from a municipal water source, it is unlikely that you would be dealing with organic matter, thanks to rigorous purification methods. 

what is TDS and how does it work

You could also look at TDS as measuring the amount of ions present in water. While it’s not a hard-and-fast rule, many of the more beneficial dissolved solids are cations, whereas the contaminants are anions. For example, calcium, potassium, and magnesium are all cations but nitrates, chlorides, and sulfates are anions. 

Is higher TDS in water better?

In the water community, there has been a recent push towards waters with high TDS. Salespeople will insist that certain water brands are superior to others because of high TDS, and some self-proclaimed water gurus have even used TDS level to malign water brands, claiming that low TDS equates to poor quality water.

This is simply not true. TDS alone is not an indicator of the quality of water. A proper analysis requires knowing where the dissolved solids are sourced from. 

How much TDS in water is healthy?

Unless you know what kind of dissolved solids are in your water, it’s hard to say what a healthy TDS level is. For example, a mineral water with a TDS between 50-150 is probably very healthy, because you can be assured that the dissolved solids are benign minerals. However, tap water that has a strong odor and is delivered through old pipes could also have a TDS between 50-150, and that may be an indicator of more salts and metals. 

Which TDS water is good for drinking?

The best water for drinking is usually under 300ppm (read on for more information about the measurement “ppm”). However, anything over 250ppm raises concerns about the number of minerals and contaminants. It could indicate that there are specific impurities over the legal limit, or it could lower the efficiency of water heaters and filters by leaving mineral deposits on household appliances and utilities. 

If your water is coming directly from your pipes, a TDS under 50ppm could also be cause for concern, because that could indicate a low pH, which would mean that the water could be leaching metals from pipes, giving it a bitter taste. Luckily this isn’t the case if your water is coming straight from a purifier, like Wisewell. In that case, low TDS simply signifies high purity.

So, under 300ppm is best - but you might be curious to know how an even higher TDS might affect your water: Once your water reaches 500ppm, there is a greater likelihood for concentrations of contaminants such as lithium and aluminum, and water over 1000ppm could contain man-made chemicals and be slightly saline. 

TDS standards for drinking water

In the United States, TDS falls under the EPA’s “National Secondary Drinking Water Regulations” (NSDWRs). These are non-mandatory and unenforceable guidelines for substances that mainly affect water in aesthetic ways, such as taste, color, and odor. TDS is included in this secondary set of regulations because it does not directly measure specific contaminants and only gives a general idea of the composition of your water. Individual contaminants with known adverse health effects are controlled via Maximum Contaminant Levels (MCLs), which are enforced by law.

The EPA now suggests that all drinking water have a TDS of 500ppm or below. Anything over that could give water an unpleasant taste or color, which the EPA is concerned could cause people to lose faith in their water source, whether or not it is contaminated with some of the more dangerous dissolved solids.

The WHO has also made suggestions for TDS level, though their guidelines have historically been higher than those put forth by the EPA. Originally, the upper limit for TDS was 1500ppm, but in 1984, they lowered the guideline to 1000, because the taste of water above that level was hard to handle.

Are TDS and hardness the same?

“Hard” water is water that has a lot of minerals, so while TDS and hardness are not the same, they are intrinsically linked. TDS determines whether water is hard or not: At a higher TDS, water becomes hard and leaves residue on faucets, pipes, and boilers.


TDS is usually measured using ppm or mg/L.

What does ppm mean?

Ppm stands for “parts per million” and it is a dimensionless measure that describes the amount of a certain substance that is present in a solution. For example, if TDS is 1ppm, you can imagine that there is one drop of dissolved solids for every million drops of water.

Sometimes solutions are measured using ppb or parts per billion. When working with both ppb and ppm, keep in mind that 1ppm = 1000 ppb.

Are TDS and ppm the same?

Ppm is the unit of measurement that is most commonly used to describe TDS. So while they are not synonyms, they are both used to define the level of contaminants in a solution.

How do I calculate ppm?

In order to calculate ppm, you have to measure both the substance you are interested in analyzing and the substance in which it is diluted. You also must choose a metric to measure. For example, you could measure the volume of both substances or the mass.

Are ppm and mg/L the same?

Ppm and mg/L are technically not the same, since ppm measures mass against mass or volume against volume, whereas mg/L measures mass against volume. However, for water, 1ppm = approximately 1mg/L, so they are used interchangeably.

How TDS is calculated

There are a few different ways that you could measure TDS, ranging from inexpensive and imprecise to pricy and specific.


The easiest way to get a ballpark idea of your water’s TDS is to simply use your senses. Observe the sight, smell, and taste of the water and see if you can deduce where it lies on the TDS spectrum. For example, if the water is salty, it likely has a very high TDS. If blue-green, gray, green, or white scale forms on faucets, curtains, or glasses, that could also indicate a high TDS. Other indicators of high TDS include crystals forming in boiling water and difficulty getting soap to lather. On the other hand, if water has a low TDS, it might have a very flat, bitter taste or (if it’s coming through metal pipes) a metallic tang.

A boring, flat taste is customary for water that has been purified using reverse osmosis, because the filtration process brings the TDS level to zero. That’s why some filtration systems that use RO (such as Wisewell) remineralize their water after purification.

TDS Meter

If you want a more scientific method of measuring TDS beyond simple observation, you can try using a TDS meter.

How TDS meters work

TDS meters work by measuring the conductivity of water. They are handheld devices that give a TDS reading right at the water source in a matter of seconds. They are relatively inexpensive - they usually cost under $100.

Are TDS meters accurate?

Because TDS meters measure conductivity, they can only be partially accurate when it comes to measuring true TDS. Not all dissolved minerals will be combinations of NaCl or KCl, which are the compounds measured via conductivity, so if you’re looking for a more precise gauge, keep reading.

Which TDS meter is best?

The best TDS meter is arguably one that already comes with your water purifier. For example, Wisewell has sensors built into the device that measures the TDS of both your tap water (the “before” water) and the purified Wisewell water (the “after” water). That data is then sent to the Wisewell app, where it can be easily analyzed alongside filter life, sustainable impact, and financial savings.

Testing Kit

There are a few different websites that offer testing kits. The kit arrives at your residence with all the instructions on how to collect a sample. You can then ship that sample to the lab, and the final report will show contaminant levels. The report also usually offers suggestions on how to treat any problems with your water.

Certified Water Testing

There is room for error with a testing kit, however, so it may be a better idea to do a certified water testing, where a water professional comes to your home and takes the sample for you.

Solutions to Unsatisfactory TDS

No matter what method you use to determine TDS, you may discover that your water is not up to par. Luckily, there are multiple ways to filter your water and adjust your TDS.

Distillation and Deionization

Distillation and deionization both remove minerals from your water, ultimately lowering the TDS. While there are major differences between the two processes, the results are very similar. Deionization, however, only works on ionic contaminants (cations and anions).

Reverse Osmosis

Reverse osmosis is the most effective way of lowering TDS. It removes 99.9% of dissolved solids. This is why reverse osmosis is one of the key steps in Wisewell’s Full Spectrum Filtration. Wisewell brings TDS down to essentially 0ppm and then adds minerals via a Maifan stone filter, so that you can be assured that all the dissolved solids measured through the Wisewell app are beneficial minerals. 

Learn more about the ways in which Wisewell filters and remineralizes your water here.

What is Total Dissolved Solids (TDS)?

Get Informed | Total Dissolved Solids (TDS)

TDS and PH

Secondary Drinking Water Standards: Guidance for Nuisance Chemicals


Understanding Units of Measurement

How to Calculate PPM

العودة إلى بلوق