TDS Meters

Total Dissolved Solids

Total Dissolved Solids (TDS) are the total weight of all solids (minerals, salts, or metals) that are dissolved in a given volume of water, Expressed in milligrams per liter (mg/L), or In parts per million (ppm).


The lower the TDS level in the water, the more efficiently your body's cells actually get hydrated by the water you drink. The higher the TDS level in the water, the greater the probability of harmful contaminants that can pose health risks of hinder the absorption of water molecules on the cellular level.

The US EPA's Maximum Containment Levels of TDS for human consumption is 500ppm

Use a TDS Meter to:

  1. Check the performance of your water filter
  2. Check for hardness (1 grain=17ppm)
  3. Make sure you always drink pure water
  4. Know when to change your water filter, use a TDS meter!

What is a TDS meter and how does it work?

A TDS meter is basically a electrical charge (EC) meter whereby two electrodes equally spaced apart are inserted into water, and used to measure charge. The result is interpreted by the TDS meter and converted into a ppm figure. If water contains no soluble materials and is pure, it will not conduct a charge and will therefore have a 0 ppm figure. Conversely, if the water is full of dissolved materials, it will conduct a charge, with the resulting ppm figure being proportional to the amount of dissolved solids. This is because all dissolved solids have an electrical charge, which allows conduction of electrical charge between the electrodes.  

In reality, the most accurate way to measure TDS of water in a laboratory setting would be to boil the water until there is none remaining, and then to weigh the remaining material. This of course is totally impractical for the lay person, as accurate scales and special equipment would be required to achieve such measurements. The TDS meter is therefore the next best device to achieving an estimated TDS reading.

What can a TDS meter be used for?

As well as measuring the TDS of our drinking water supplies, a TDS meter can be used for measuring;

  • Fish tanks and aquariums

     Fish require a specific TDS and pH similar to the natural environment in which they live. Freshwater fish require less than 400ppm, with some other freshwater fish requiring less. Saltwater fish require TDS readings of between 5000 and 50000ppm.
  • Hydroponics

    A TDS meter is a useful aid for quickly measuring the nutrient concentration of a hydroponic solution.
  • Pools and spas

    A low TDS reading can help prevent maintenance issues, skin irritation and algal blooms.
  • Colloidal silver

    There are many consumers of colloidal silver today using a TDS meter to measure their colloidal silver concentration in parts per million (ppm). The TDS meter gives a relatively accurate measurement, and is expressed in the nomenclature ppm TDS e.g., 10ppm TDS. This saves hundreds of dollars obtaining more accurate laboratory analysis which would otherwise be required.

Why should I measure the TDS of water?

In the United States, EPA regulations recommend a maximum water contamination level of 500mg/L (or TDS level of 500 ppm). If this figure exceeds 1000 ppm, the water is generally considered unfit for human consumption.

The TDS meter is an excellent means by which you can regularly test your water supply, as well as your water purification system and its performance in cleaning your water. If you notice the TDS level beginning to show an increase in your reverse osmosis or other water purification system, then it is time to change the filters or cartridges. A high TDS from tap water could indicate the possibility of hard water, resulting from a build-up of scale in pipe delivery systems.

A high TDS figure represents water which could be undesirable in taste, with a salty, metallic or bitter tasting water. Remember, the EPA's recommended maximum TDS level is 500mg/L (or 500ppm).

How do I use a TDS meter?

A TDS meter is very easy to use.

  1. Firstly, collect water in a clean glass or cup.
  2. Turn the power on to the TDS meter, and remove the cap.
  3. Insert the 2 electrodes at the end of the TDS meter fully into the water, being sure not to insert the whole unit which could cause damage.
  4. Stir the water a little using the TDS meter or shake it slightly to ensure the electrodes are fully immersed, and that no bubbles are attached to the electrodes.
  5. Wait about 5 seconds, or until the display stabilises with a constant figure. The figure that you now read is the TDS reading.
  6. After you have finished, take the TDS meter out of the water and give it a shake to ensure excess liquid is removed. It is ideal to rinse the electrodes with reverse osmosis water, to ensure that the next test does not contain contamination from the test just completed.
  7. Place the cap back onto the TDS meter to protect the electrodes. 

How do I reduce the TDS reading of my water supply?

TDS readings can be reduced by using a water purification system. Water purification systems commonly used in the home include;

  • Sediment filtration
  • Carbon filtration
  • Reverse Osmosis (RO) purification
  • Purification by Distillation
  • Deionisation

A system consisting of sediment, carbon and reverse osmosis purification all in one is recommended for the supply of clean water in general urban living. Sediment filters can be used to remove dirt and grit, and other fine particles usually to 1 micron in size. Once water has had sediment removed, it is ready to pass to carbon filtration, where chlorine and other toxic chemicals can be safely removed. The final process is reverse osmosis purification, where dissolved substances are removed by forcing the water through a semipermeable membrane, resulting in pure water.

What about mineral water?

There is a common belief that mineral water is important for our health, and that because pure reverse osmosis water contains little or no minerals, it is not an ideal source of supply for our health. This has been shown scientifically to be untrue, as all of the minerals in mineral water are a lifeless inorganic form. While they may be absorbed into circulation within our bodies, they cannot be used in physiological processes to for instance build cells. According to the American Medical Journal, the bodies requirement for minerals is largely met through foods, and not through water. Only after they have passed through the roots of plants do these inorganic minerals become organic (through photosynthesis) and capable of being assimilated into our tissues as organic minerals.

Pure water produced by reverse osmosis has an advantage, in that it removes inorganic deposits throughout the tissues in our bodies, leading to improved health. Organic minerals are not removed by pure water, and they remain in our bodies allowing smooth physiological functioning within our bodies.

To give you some idea, a single glass of fruit juice provides more beneficial minerals than 30 gallons of untreated tap water.