What Does A TDS Meter Measure


A TDS meter (Total Dissolved Solids) is an electronic handheld device that will measure solids in dilution. It will give a reading in ppm or parts per million of an unknown amount of substance dissolved in a sample. It’s used in Industry, Drinking Water, Aquariums, and Hydroponic systems in any application where the measurement called for. What does a TDS meter measure?

A TDS Meter measures Total Dissolved Solids that is the total amount of mobile charged ions, cations, or anions including minerals, salts & metals dissolved in a given volume of H2O, expressed in mg/L & ppm including anything present in H2O other than the pure water H20 molecule & suspended solids.

In the scientific world we live in, seeing is believing as long as the information is applied correctly. There are some misconceptions about the TDS meter that can be cleared up by reading this article.

How Does a TDS Meter Work

TDS or Total Dissolved Solids gives the sum of dissolved solids in a solution. The solids include for example salts, minerals, and metals. They can be organic or inorganic substances. Some of these particles in solution carry an electrical charge. The value is also called the conductivity of the water. Because the more such solids or ions are in the water, the better it conducts electricity. TDS meters typically quantify this conductivity in micro siemens or ppm.

PPM stands for parts per million the number of solid particles per one million water mixture particles.

A TDS meter provides a reading by measuring the conductivity of the dissolved ions in a solution. It does this by sending out a small electrical charge through the sample and measures the EC or Electrical Conductivity in what called siemens or mili-siemens or smaller micro siemens. Once the reading is taken, a formula is used to convert it into an estimation of the TDS. This reading can give you an indication of the quality of the water. It can also estimate concentrations of nutrients in Hydroponics, the health of Fish Aquariums, and hardness in drinking water.

It is generally used in water treatment as an indicator or a presence of a broad array of chemical contaminants that are unknown. In Professional Laboratories, solids in dilution are weighed, dried to evaporation, and weighed again for an exact measurement. The Digital TDS can give a fairly accurate and reliable reading up to plus/minus 0.01 ppm. Which is good enough for most applications.

Involving process control of waters and liquids used in Agriculture and Industry. The advantage of having a lower TDS reading in water treatment is that generally, it means you have fewer unknowns in the water.

In Tap water, those measurements can  involve minerals and salts like:                     

  • calcium
  • magnesium
  • potassium
  • sodium
  • bicarbonate
  • iron
  • zinc

According to EPA, Total Dissolved Solids in Drinking water is considered a Secondary Contaminant and not a threat to health standards but is considered more of a nuisance. The Total Dissolved Solid Meter won’t identify anything in the liquid it will only indicate that it’s there. EPA has set standards at 500 ppm or mg/l (milligrams per liter) which is the same thing in the scientific community. If you have a problem with Dissolved Solids or questionable water from a private Well, then buy a meter.

Dissolve Solids are hard to filter out. To get down to a filtering size that will remove TDS you’ll need Reverse Osmosis that can get down to 1-micron size. Most filters can’t do that.

Normally high Total Dissolved Solids lead to aesthetics, taste, and smells in drinking water but can indicate other contaminants.  The easy use of a handheld TDS meter makes it perfect to use where water quality is important to maintain conditions. The 6-inch 2 pronged devices are dipped into the solution and a readout is instantly portrayed on a battery-operated LCD screen.  Applications for TDS meters include:

  • All Water Purification Applications.
  • Reverse Osmosis.
  • Drinking-Water.
  • Water Conditioning.
  • Cooling Towers.
  • Wastewater.
  • Laboratories.
  • Agriculture

How to use a TDS Meter

Here I use the TDS for simple comparison to find the reduction rate for a Reverse Osmosis water filtration system. To do this I tested in coming Tap water against the processed water from my Berkey water filter that contains RO filters. 

In this case, I wanted to get an idea of where my processed Tap water would be under normal average use so when I check again I will be able to see that reduction rate falling over a period of time. Variable can be according to TDS, usage, or if there are more people in the house. Look what the Filter manufacturer says is the variable. In this example:

  • Base Test is the source is 158 ppm
  • The initial reduction (new Filter) by the Filter = 158 ppm -9 ppm = 149 ppm
  • which equals a 94% reduction
  • after 1 month
  • All you do is check once per month
  • you’ll know when you will have to purchase a filter
  • City water-or source water will stay constant in most cases


You know the manufacturer recommends that the filter can work for up to 3,000 liters but an easier approach would be to start off with a percent reduction and once that starts to reduce clean the filters and if that doesn’t work you then can swap out the filters. This way you can get as much out of your system without changing them needlessly or drinking partially treated water. It’s simple and fast.

Is TDS a good measure of water quality?


Aquariums use a regular filter that can only pick up material that is particle size either suspended or settable solids that can collect in the fish tank. These particles contain plant matter or fish waste. High concentrations of TDS above 250 ppm can reduce water clarity and decrease photosynthesis in aquatic plants. Keeping track of TDS in Fish Aquariums can offset toxicity problems that can destroy the Aquarium. Just about everything that enters the tank will contribute to TDS readings. A good start is around 150-180 ppm.

Fish that survive in the Aquarium live within certain parameters of TDS along with temperatures and PH that are needed as controls to keep things healthy and happy. This includes fish and plants that are happier at certain levels than other plants and fish. Compounds like Nitrates, Nitrites along with Calcium and Magnesium ions, and others that can change in an Aquarium will move the TDS level in your tank. The way to start is always from the beginning. Just like in the example I talk about above.

You need to know what the Base TDS is in the source water before it’s involved with the Aquarium. This is so you have a place to come back and compare it to overtime. If you added rocks or plants that are new. Did they make a difference in the TDS of the tank? Is there a nitrification or Oxygen problem in the tank? All these can be discovered through the TDS readout either done by you or on an automatic display.

If your Tap water is too high consider a water filter.

  • Then, continuously monitor the TDS meter as your aquarium runs and as you add any kind of substance to your water.
  • Once you have determined the average TDS of your aquarium from observing for a few days
  • Use some testing to make sure all of the individual compounds the one you will look at when operating a fish Aquarium are at their desired levels like nitrate, nitrite, GH, KH, chlorine.
  • If all of these levels are correct, the average TDS you’ve observed is your aquarium’s ideal TDS level.

If you test for TDS every day or better have a Constant Online Digital Monitoring System and can see indicator levels before things start to happen. The approach will save money and time for testing the Aquarium for changes in the molecular part. You must need a good solid base start to compare to. A spike in the level would indicate that one of the compounds that were measured in the initial testing is rising at a small molecular level. Then you test for those compounds. The advantage of having a lower TDS reading is that generally, it means you have fewer unknowns in the water tank.

Organic waste will also raise TDS unlike what most people think, organic waste doesn’t transform instantly into just ammonia. Breakdown of organic waste goes through intermediate stages that release carbohydrates, lipids, proteins, nucleic acids into the water column. A breakdown will be seen on the daily Total Dissolved Solids measurement.


How to Measure Nutrients in Hydroponics


A TDS/EC Meter measures the concentrations of the nutrients solution in Microsiemans and PPM. The meter measures the EC by passing a small amount of electricity passed between the two probes that normally found on the portable TDS/EC meter. From the measurement of electrical conductance, EC, farmers of Hydroponics systems are able to infer the concentration level of the Nutrient Solution. In America,  Basically, the two measurements are interchangeable. An EC conductance value in Microsieman can be multiplied by 0.5 and converted at PPM value.

The meter has this capability using the software inside the meter. They will use a standard 0.5  so that the result is delivered in Parts Per Million. An example would be if the EC is equal to 800 micro siemens then the result would be multiplied by 0.5 and equal to 400 ppm. The Nutrient concentration with the conversion factor would be 400 ppm in the system. Some more expensive models are calibrated like PH meters when used for more detailed results.

Calibration is important when using EC/TDS meters. You should calibrate with a value close to your sample’s conductivity. Conductivity standards are salt solutions for which the conductivity and temperature dependence are known. There are also factory calibrated meters that will last the life of the meter without the need for calibrating. Concentrations of nutrients are dependent on what is growing in the system so different amounts and concentrations are used and recorded so that the results can be used over and over. Pure water is used to check calibrations for the meters.

A very good Combination PH/EC/TDS/ Salinity/Temp Meter Apera Instruments PC60 Premium 5-in-1 Waterproof pH/EC (Conductivity) /TDS (ppm) /Salinity (PPT) /Temp. Multi-Parameter Pocket Tester Kit, Replaceable Probe It’s a little more serious than a Digital Pen type of probe. Check it out here on Amazon.


 Industries Use TDS Measurement

In any industry where exact specifications are needed to produce a product or are used in the manufacturing of a product detailed instruments and technicians to use those instruments for a controlled process. The measurement of Total Dissolved Solids is important in many processes that involve stringent controls where specifics are necessary like in:

Food & Beverage – While the industry is a complex and diverse set of businesses supplying the world’s food supply.  Anytime there is food preparation, water comes into the equation.  Knowing what that water contains is vital to meeting the numerous regulations and standards to providing a safe food supply.

In the world of Coffee manufacturing, TDS testing includes compounds chlorogenic acids, esters, and caffeine, as well as organic acids like citric, malic, and lactic acids. These compounds are what make up a coffee’s body, aroma, and flavor and comprise a coffee’s TDS measurement which is part of the process in making a good cup of Joe. TDS is an emerging and increasingly more popular modern metric for controlling coffee strength and taste. Same with Beer Brewing that commonly uses Reverse Osmosis then add minerals that were used in the water purification process.

Industrial – When treating water in industrial settings, large scale build-up, corrosion or even bacteria growth depending on the application can have terrible consequences.  To eliminate these problems treating your water and knowing your water’s content you are using is critical.  This is done by constant monitoring and controlling your water treatment process during production.

Pool and Spa – Anytime there is a body of water, especially one you are going to have contact in, expert maintenance is of great importance. Since there are different methods of keeping these environments clean, metering TDS, pH, and ORP helps you determine if your sanitation methods are working properly constantly.

Window Cleaning and Carwash – ensuring that something not only is clean but looks clean, then having ultrapure clean Spotless rinses every time for RV Motorcycles and detailing your vehicle where water is of paramount importance The only way to do this is by removing all TDS from the water, and the only way to know what has happened is with in-line monitors who measure both feedwater, soap addition, and product water. Water issues are dependent on location and will vary by water source and by carwash, some of the most common water contaminants/concerns impacting carwash operations include:

  • Water hardness, which is primarily comprised of magnesium and calcium but can include iron and manganese as well
  • Total dissolved solids (TDS)
  • Silica
  • pH.

Potassium, iron, oil, and surfactants are also generally found at carwashes TDS is the one found in most businesses. Calcium and Magnesium hardness is probably the biggest [concerns] for carwashes

Water Treatment Industry -Conductivity or TDS, the most widely used control parameter for other applications, measures caustic or acidic solution strength PH control. Conductivity also monitors process completion to identify product variation and control of chemical additives.

Inductive conductivity, sometimes referred to as electrodeless or toroidal, remains the industry’s primary choice due to sanitary design standards. Conductivity also determines filtration media efficiency by gauging the dissolved, ionic constituents before and after the filtration process.

Environmental Industry-Electrical conductivity (EC) and TDS are other ways to evaluate water quality, since the increased presence of total dissolved solids (TDS), is sometimes as expressed by EC, may be an indicator of pollutants.

TDS can be affected by the effluents of Sewage Treatment Plants. Higher results of TDS can alter the growth of aquatic organisms and disrupt water balance.

Lower TDS concentrations can limit the growth of organisms. EC can have a negative impact on photosynthesis. This is because increased solids at the discharge of Wastewater plants can make water murkier in the receiving stream, which slows down the rate of photosynthesis.

High levels in TDS that are Salts can contribute to Acidity and high levels of if the level of Carbonates in TDS could contribute to an increase in alkalinity, which helps protect against acidity problems in the environment. Knowing these TDS results can give better control improvements over parameters. 


JimGalloway Author/Editor











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