Water is a substance composed of H2O molecules. It is one of the most essential compounds for life on earth. Humans use water in many different ways; for drinking, washing, other household needs, industrial needs, etc. Hence, measuring the water quality is very important. There are various chemical and physical parameters measured regarding water quality. Some chemical parameters include pH, electrical conductivity, total solids, total dissolved solids (TDS), and hardness. Some physical parameters include color, odor, etc. TDS or total dissolved solid in water refers to inorganic salts and some trace amounts of organic matter that are dissolved in water. Hard water is water that has a high mineral content. The main difference between TDS and hardness is that TDS include inorganic and organic substances that cannot be filtered through a filter paper whereas hardness is due to the presence of magnesium and calcium salts of carbonate, sulfate and chloride.

What Is TDS?

Total dissolved solids (TDS) describes the amount of dissolved material in a water sample. TDS is typically represented in terms of milligrams of material per liter of water (parts per million).

  • The biggest contributors to TDS are minerals such as calcium, magnesium, sodium, chlorides, bicarbonate, and sulfate.
  • Some dissolved metals and organic material may also contribute to TDS.
  • TDS is a good measure of the overall quality of water, but does not indicate the relationship between ions, or if the water is safe to drink.

A lower TDS result indicates more pure water.

Measuring TDS:

Most people search for how to measure TDS. There are two ways through which you can do this.

  1. Gravimetric Method
  2. Electrical Conductivity Method

In the gravimetric method, the liquid evaporates. It is a traditional method and time taking process. The residue that is left behind after evaporating the liquid is TDS and it is weighed to measure the quantity of TDS. Although this method takes time but perfects to get accurate results.

In the electrical conductivity method, a TDS meter measures the TDS of water. Here most people have questions in mind that what does a TDS meter measure and how to use a TDS meter? The simple and accurate answer is it measures the presence of everything except H2O in water. The concentration of ions present in water is directly proportional to the electrical conductivity of the water sample. We measure the TDS through the TDS meter for different purposes. It is done for river, lake, and stream testing, swimming pools, agriculture, and hydrophobic cultivations, and other water-related problems.

What Is Water Hardness?

Water hardness is the sum of calcium and magnesium present in water and is most commonly measured in terms of grains per gallon.

  • Hardness is also sometimes represented in milligrams per liter, or parts per million (PPM).
  • Hard water gets its name from excessive amounts of minerals that make it more difficult for soap to properly clean – leaving residue behind on dishes and clothing.
  • High hardness causes deposition of calcium carbonate (scale) on heating surfaces and can clog pipes, valves, and screens over time.

A lower amount of hardness in water is desired in almost every situation. Water with a total hardness exceeding 3.5 grains per gallon is considered hard.

There are two types of water hardness:

  1. Temporary Hardness
  2. Permanent Hardness

Temporary Hardness:

Magnesium and calcium carbonates are dissolvable in water. When these bicarbonates minerals are dissolved or present in water, they make the water temporary hard. These minerals form carbonate and bicarbonate anions along with calcium and magnesium cations when mixed in water. Water hardness through these bicarbonates minerals is temporary and can be removed by boiling water or adding lime in hard water.

Permanent Hardness:

Permanent hardness of water occurs when sulfates and chlorides of calcium and magnesium are dissolved in water. When the water is heated, these minerals are not hasty. That’s why permanent hardness cannot be removed by adding lime or boiling water. To remove permanent hardness, you need to use a water softener.

Measuring Water Hardness:

Measuring the water hardness is very easy. It is measured in mol/L or mmol/L units. The simple method of testing water hardness testing is through a soap test kit. You required a little bottle or testing kit with a line marked on it. Add water to the line and then add a drop of soap. After this shake the bottle and look for suds. If suds appear, it means water is good and if not that means it is hard water. Adding more drops of soap will lead to more degrees of hardness.

Difference Between TDS and Hardness


TDS: TDS stands for total dissolved solids.

Hardness: Hardness refers to the presence of a high mineral content.


TDS: TDS is caused by inorganic salts and dissolved organic matter.

Hardness: Hardness is caused by either magnesium and calcium carbonates or their sulfates and chlorides.


TDS: TDS is measured from ppm units.

Hardness: Hardness is measured from mol/L or mmol/L units.


TDS: TDS is measured by either gravimetric method or electrical conductivity analysis.

Hardness: Hardness is measured using laboratory experiments or hardness testing kits.

Effects or Uses

TDS: TDS measurements are useful for river, lake and stream testing, swimming pool and spa maintenance, agriculture and hydrophonic cultivations, aquarium maintenance, etc.

Hardness: Hardness causes the formation of a white precipitate on container surfaces, alter the taste of water, the formation of soap scum, etc.

How Can You Tell If You Have High Hardness or TDS Issues?

Detecting Hardness in Your Water

  • Hardness can be measured using a test kit or by having the water tested in a lab. Hard water will deposit distinctive white residue (scale) around sinks, shower heads, and on dishes.
  • Hardness varies by region but is usually more consistent across a particular area than TDS is a water testing kit will typically use color changing test strips and a chart that can help you determine the approximate level of hardness in your water.

Detecting TDS in Your Water

  • The best way to measure the TDS in your water supply is to use a TDS meter. These meters work by sending a pre-determined electrical current through the water, and then measuring how much that current is reduced while passing through the water.
  • TDS varies greatly in different regions of the country and can even be extremely different between one town and the next if they are drawing from a different natural water source.

You can also have your water tested in a certified laboratory with an Antunes Water sample analysis kit. The test results will include TDS and hardness among other relevant metric sand will be sent to you along with a custom product recommendation from the Antunes Water Team.

Addressing High Hardness and TDS in Your Water

Fortunately, there are ways to mitigate the undesirable effects of high hardness and TDS.

Water softeners are an excellent choice for removing hardness from your water, and if installed at the water’s entry point, can provide softened water for your entire home.

The best choice for reducing the TDS of your water is a residential reverse osmosis system. Reverse osmosis systems use pressure to force water through a semi-permeable membrane, separating the dissolved solids from the water at the atomic level.

The quality of your water is important to the quality of your life – and you can take control of it today. Antunes Water offers a residential five-stage reverse osmosis system as well as whole home softener systems. These systems complement each other and together will help you to achieve the excellent water quality that you desire.