What is Total Dissolved Solids (TDS)?

July 12, 2021

What is total dissolved solids (TDS), how to measure TDS and how to reduce TDS

About the author:

Brian Campbell is the founder of WaterFilterGuru.com, where he blogs about all things water quality. His passion for helping people get access to clean, safe water flows through the expert industry coverage he provides. Follow him on twitter @WF_Guru or contact him by email [email protected]

One of the simplest ways to determine your water quality is to measure its TDS. Total dissolved solids, or TDS for short, are dissolved ions, including salts, minerals and metals, that can be found in all non-pure water sources. 

Why is it so easy for TDS to get into water? H2O, or water, is a good solvent. This means it is capable of holding onto impurities that it might encounter on its journey into your drinking glass. 

Total dissolved solids in water is not necessarily a bad thing. Some TDS can be healthy, while some are more harmful. This guide will discuss the most common types of TDS and their sources, and share how to measure TDS in water. 

Types of Total Dissolved Solids in Water

Now you know the total dissolved solids definition, let’s take a look at the types of TDS you might find in your water. There are hundreds of types of TDS, but they generally fall into four categories: minerals, salts, dissolved metals, and other organic matter. 


Minerals such as magnesium, calcium and potassium get into water from natural sources. When water in rivers, streams and lakes come into contact with mineral-rich rocks, small amounts of these minerals are released into the water. Minerals improve water’s taste and contribute towards your daily RDI. 


Low levels of salts may occur naturally in groundwater. Salt levels may also be affected by human activity, such as de-icing roads, fertilizer and water softener use, and even sewage contamination. 

Dissolved metals

Dissolved metals mainly make their way into water through pollution. Industrial waste and human activities such as mining, can both result in the leaching of metals into drinking water. Rock or soil material may contain small amounts of metals, and some types of metal pipes can also contribute to water’s dissolved metal content. 

Organic matter

Dissolved organic matter usually enters into water as a result of the natural decomposition of algae and plant material. In municipal applications, the majority of natural organic matter is removed from water during the treatment process

Sources of TDS in Water

Total dissolved solids can come from all manner of sources. Materials may leach into water from sewage, water treatment chemicals, agricultural runoff, or industrial wastewater. Natural sources, like soils and rocks, may also contain TDS. Urban runoff, or the flow of rainwater in urban landscapes, can carry TDS, and even the pipes and plumbing materials used to carry water to a home may be a TDS source. 

Remember, TDS is not necessarily a bad thing. “Beneficial” TDS like minerals can be found in environmental features such as carbonate deposits and mineral springs. Salts, a common type of TDS mentioned above, may end up in drinking water from seawater intrusion or even from de-icing substances on urban roads. 


How to Measure Total Dissolved Solids

Keeping an eye on water’s TDS may be necessary for a number of reasons. Perhaps one wants to solve a water hardness issue, and measuring TDS will keep track of success. Some may also want to understand why their water tastes bitter, or check that their health is not at risk from the stuff that comes out of the tap. Those with a pool or a spa might want to monitor TDS levels to make sure there are no issues with maintenance. 

There are two options for measuring TDS in water: the laboratory option and the at-home option. The laboratory option requires materials and equipment the average person will not own, so the at-home or in the field option — using a total dissolved solids meter — is the better choice.  

Total Dissolved Solids Meter

A total dissolved solids meter is a handheld device that can be used to give a TDS reading of a water source. Searches on line reveal TDS meters priced between $10 and $100, depending on the brand and the complexity of the device.

Dissolved solids naturally increase water’s conductivity. A TDS meter, therefore, measures the conductivity of a water sample and uses this figure to determine water’s TDS level. This level is measured in parts per million (ppm) or milligrams per liter (mg/L).

It is important to note that while a TDS meter will measure the concentration of TDS in water, it will not explain what contaminants that water contains. Additionally, a TDS meter can only measure dissolved solids. Some contaminants, like certain metals, chemicals, pharmaceuticals and pesticides will not be picked up by a TDS meter. For more clarity and precision as to what is in a water source, consider water testing. 

RELATED: What is Total Suspended Solids, or TSS?

Is High TDS Water Harmful?

It would be wrong to instantly conclude that high TDS water is harmful, as it depends on what type of TDS that water contains. For instance, a TDS reading could be particularly high, but it might simply be because that water has a high mineral content. 

EPA guidelines dictate that a ppm of more than 500 is too high for total dissolved solids. Water containing more than 1,000 ppm of TDS should not be consumed. 

If water has a TDS reading of more than 500, it is worth arranging to get it tested, which will outline exactly what is causing this. 


How to Reduce Total Dissolved Solids

There are a number of approaches to take to reduce water’s TDS content. These are:

Reverse osmosis

A reverse osmosis system uses multiple filtration stages and a semi-permeable membrane to reduce more than 99.9% of TDS. This type of treatment system is common water treatment plants and wastewater treatment plants. That said, it can also be installed underneath a kitchen sink or a home’s point of entry. One can also find countertop reverse osmosis filters that are powered by electricity. 

Water distillation

A countertop water distiller uses the highly effective method of distillation to remove TDS from water. During distillation, water is boiled until it evaporates. The majority of total dissolved solids are unable to evaporate with water, and they are left behind in the boiling chamber. Water then condenses into a clean carafe, ready for drinking. 


Finally, deionization uses an ion-exchange process where water passes through both a positively and negatively charged resin bed, which attracts both cations and anions, removing them from the water. Deionization only works for ionic contaminants, so this process would require the use of another purifier, such as a reverse osmosis system, to remove the non-ionic impurities. 

About the Author

Brian Campbell

Brian Campbell is the founder of WaterFilterGuru.com, where he blogs about all things water quality. His passion for helping people get access to clean, safe water flows through the expert industry coverage he provides. Follow him on twitter @WF_Guru or contact him by email [email protected].

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