TDS meter

Water's considered a “universal solvent” because of its ability to dissolve and absorb molecules from various substances. The amount of dissolved particles in a particular volume of water is called the total dissolved solids (TDS) level. We'll explain how you and measure and reduce the TDS level of your water.

What is TDS in water?

Total dissolved solids (TDS) are the amount of organic and inorganic materials, such as metals, minerals, and ions, dissolved in a particular volume of water. When a solvent, such as water, encounters soluble material, particles of the material are absorbed into the water. TDS in water can come from just about anywhere, including minerals in springs from a water source, chemicals used to treat the water supply from sewage systems, runoff from road salts and yard chemicals or fertilizers, even the plumbing in your home.

How is TDS measured?

Testing your water using a TDS meter is the easiest way to measure for total dissolved solids. Some filtration systems are equipped with a TDS meter to monitor the levels periodically. Also, your water supplier is required to test and maintain reports regarding water quality and provide them upon request. However, these reports do not show reasons for high TDS that are specific to your house, such as corroded pipes.

Total dissolved solids (TDS) is measured as a volume of water with the unit milligrams per liter (mg/L), otherwise known as parts per million (ppm). According to the EPA secondary drinking water regulations, 500 ppm is the recommended maximum amount of TDS for your drinking water. Anything measurement higher than 1000 ppm is an unsafe level of TDS. If your TDS reading exceeds 2000 ppm, then a filtration system may be unable to handle it.

TDS Water Chart

 <50-250 ppm Considered low: missing in some of the minerals that are beneficial to your health
300-500 ppm Perfect: This level is the sweet spot for TDS in drinking water
600-900 ppm Not great: Consider a reverse osmosis system to remove your TDS
1000-2000 ppm Terrible: Not recommended or safe for use
>2000 Worst: A TDS level above 2000 ppm is completely unsafe and household filters can not handle this level of contamination


How to measure TDS

  • Measure the TDS of raw feed water by submersing the tester's probes into a cup or glass of TAP water. Record the results.
  • Measure the TDS of your RO water by filling a cup or glass with RO water (from RO faucet) and submersing the tester's probes into the water. Record the results. 
  • Calculate percent rejection using the following formula:

TSD Meter Calckulator

Example: Tap TDS = 260 ppm RO TDS = 20 ppm Rejection = [(260 - 20) / 260] x 100 = [240/260] x 100 ≈ (.923) x 100 = 92.3

Note: If your RO system is new or the membrane has been replaced, do not test the first tank of RO water. The first tank will contain sanitizer and possibly carbon fines from your new filters that will cause a false reading.

Why should you measure total dissolved solids?

Because quality water is pure, absent of taste, odor and color, testing the level of TDS in your water can be a great way to analyze the overall quality of your water.

  1. Taste: High levels of TDS affects the taste of your drinking water. Depending on the type of dissolved solid, water could cause a bitter, salty, or even a sulfuric taste or odor.
  2. Health: High TDS water could be safe to drink. However, some substances, such as lead or copper, are health hazards.
  3. Filter maintenance: Water filtration systems are a great solution to total dissolved solids, but they do not last forever. Routine testing for TDS can provide assurance that your filter is working properly.
  4. Plumbing and appliances: Water that contains high levels of dissolved calcium and magnesium can cause high TDS levels and hard water. Hard water collects in pipes and forms scale and buildup, which result in costly replacement for pipes and reduce the life of your appliances.
  5. Pools: The hard water resulting from elevated levels of total dissolved solids can result in clogged pipes for your pool as well.
  6. Cooking: Though not detrimental to your health below 1000 ppm, cooking with elevated TDS can change the taste of food.
  7. Cleaning: If your dishes have water spots no matter how well you clean them, if your clothes fade in the wash, and if you have buildup in your sinks, tubs, and faucets, then it may be time to test your water for total dissolved solids.

Health effects of high TDS in drinking water

Though an elevated level of TDS can affect the taste of your water and the health of your appliances, it is not harmful to your health. In fact, some minerals that cause elevated TDS, such as magnesium and calcium, are beneficial to your health. However, readings above 500 ppm require further investigation for toxic particles such as heavy metals, and readings of 1000 ppm are completely unsafe for human consumption.

Is low TDS water harmful?

TDS water readings of 0 TDS are not bad for your health. Low TDS means you have high-quality water. But low TDS may cause your water to have a flat taste. Rainwater is naturally devoid of TDS due to evaporation. Levels between 300-500 are the best TDS levels for drinking water.

Effect of TDS water on plants

The effect of total dissolved solids on your plants and your fish tanks

If you are growing plants, vegetables, or flowers through hydroponics, then total dissolved solids play an important role in providing nutrients to your plants. Two substances often causing high TDS are potassium and nitrates, which are great for your roses. You may have even seen your grandparents putting banana peels at the base of rose plants for the same effect. Flowers should have around 1000-1100, ppm while vegetable plants should have around 900-1000 ppm. Knowing the types of dissolved solids, however, is important when watering vegetable plants. If toxic ions are present, they will be absorbed by the plant.

If you have fish, it is best to keep them in a solution of water with total dissolved solids similar to their natural habitat. High TDS can wreak havoc causing cloudy water and a lack of penetration for sunlight and, therefore, photosynthesis for aquatic plant life. It can also raise the temperature, which can be harmful to some species.

How to reduce TDS in water

A water treatment system is a great way to reduce or remove TDS from your water, especially if your TDS is above 500 ppm or higher than you would like for the taste of your water. Although TDS can determine if your water contains a certain level of dissolved solids, it can not determine the types of substances. If you don't know what's causing issues like odors or spots on your fixtures, then it can be difficult to choose the best filtration system to solve the issue. Using a home water test kit helps you determine the makeup of your water and analyze whether further action is needed beyond a water system.

Below are three TDS water filters we recommend to reduce high levels of total dissolved solids in your tap and drinking water:

1. Reverse osmosis (RO) system

A reverse osmosis system is one of the most comprehensive filters to remove contaminants. This system forces water through a semipermeable membrane that eliminates total dissolved solids. It also uses a sediment and carbon filter to remove other forms of contaminants.

Read more: What is a reverse osmosis system and how does it work?5 of the Best Reverse Osmosis Systems

2. Water Distiller

A water distiller removes contaminants through the same process used in nature, evaporation. As water evaporates, contaminants are unable to evaporate. This is why rainwater is pure quality water. The system mimics this phenomenon by distilling water leaving the contaminants behind.

Read more: What is a Water Distiller and How Does It Work? | Is Distilled Water Safe to Drink?

3. Deionization (DI) system

Deionization systems remove total dissolved solids through ion exchange, using resins that control the electrical charge of ions. Water ions are used to replace charged ions from total dissolved solids. The water produced is highly pure, so DI cartridges are often referred to as high purity filters.


  • The TDS shown as 035. Please tell me whether it’s suitable for drinking purpose?


  • Hello Mike,

    You can purchase a handheld TDS meter that will provide you with a general idea of the TDS levels present in your water.

    However, if you are interested in a more thorough breakdown of the contaminants in your water and the levels of the various dissolved solids in your water, you should perform a more in-depth water analysis. This test will have you gather samples of your water and mail them to a certified laboratory. They will then provide you with a complete breakdown of the minerals, metals, and inorganics in your water. We recommended this test:

    Hopefully this helps!

    John Woodard, Master Water Specialist on

  • How do you get a TDS breakdown test and where


    MIke on

  • Thanks for the information. 👍


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