How to Measure The Levels Of Total Dissolved Solids in Your Water


Even the best water purification systems on the market require monitoring for total dissolved solids to ensure the filters and/or membranes are effectively removing the bacteria and unwanted particles from your water. Besides drinking water, where a lower level of TDS (purer water) is preferred, a TDS level is specific for each application and particular usage.

Fish and plants require water with widely varying TDS levels, most of which are higher than what we deem to be healthy drinking water for people. TDS in water supplies originate from natural sources, sewage, and urban/agricultural run-off.

What Are Total Dissolved Solids?

TDS, or total dissolved solids, is the term used to describe the inorganic salts and small amounts of organic matter present in solution in water. The principal constituents are usually:

  • calcium
  • chloride
  • hydrogencarbonate
  • magnesium
  • nitrate anions
  • sodium and potassium cations and carbonate
  • sulfate

Total dissolved solids are differentiated from total suspended solids (TSS), in that the latter cannot pass through a sleeve of 2 micrometers and yet are indefinitely suspended in solution. Salts used for road de-icing can also contribute to the TDS loading of water supplies. Concentrations of TDS from natural sources have been found to vary from less than 30 mg/L to as much as 6,000 mg/L, depending on the solubilities of minerals in different geological regions.

Why Should You Measure the TDS Level in Your Water?

The presence of dissolved solids in water may affect its taste. The palatability of drinking water has been rated by panels of tasters in relation to its TDS level as follows:

  • EXCELLENT –  less than 300 mg/L
  • GOOD –  between 300 and 600 mg/L
  • FAIR –  between 600 and 900 mg/L
  • POOR – between 900 and 1,200 mg/L
  • UNACCEPTABLE – greater than 1,200 mg/L

Parts per million (ppm) is the weight-to-weight ratio of any ion to water.

The EPA Secondary Regulations advise a maximum contamination level (MCL) of 500mg/L (500 parts per million) for TDS. However, numerous water supplies exceed this level and when TDS levels exceed 1,000mg/L it is generally considered unfit for human consumption. A high level of TDS is an indicator of potential concerns, and further investigation should be done. Most often, high levels of TDS are caused by the presence of potassium, chlorides and sodium.

Water with extremely low concentrations of TDS may also be unacceptable because of its flat, insipid taste. Certain components of TDS can influence corrosion or encrustation in water-distribution systems. Excessive scaling in water pipes, water heaters, boilers, and household appliances such as kettles and steam irons can occur with high TDS levels (>500 mg/L). High TDS levels can shorten the service life of these appliances and others. Reliable data on possible health effects associated with the ingestion of TDS in drinking water are not available.

Measuring Water TDS at Home

TDS handheld meters are a great and generally inexpensive way to test the water quality in your home at any given time. They come factory calibrated and are ready to use out of the box, being designed to stay consistent. A TDS meter is based on the electrical conductivity (EC) of water. Recalibration is necessary after prolonged usage and you will need a commercial standard Na-Cl-based solution. Here are a few tips on how to care for your TDS meter:

  • always rinse the sensor pins in distilled water and allow to air dry before replacing the cap
  • clean the electrodes to prevent residue build-up after repeated usage in high TDS water
  • do not drop or completely submerge the unit in water or dip beyond the maximum immersion level
  • do not store the unit in high temperature or direct sunlight
  •  if the tip is heavily fouled with organic material, soak it in alcohol or bleach; gentle wiping with a soft, nonabrasive cloth may also be acceptable
  • make sure that the battery compartment and probe gasket ring are firmly tightened before submersing in water
  • pH and ORP electrodes must be stored in a special storage solution
  • TDS electrodes should be stored dry
  • the batteries may need to be replaced after extended usage or lifespan
  • when necessary, clean the electrodes by soaking the tip in an acid (e.g., vinegar or diluted hydrochloric acid) and then rinsing well in water

How Do You Reduce the TDS in Your Water?

Common water filter and water purification systems that have proven to reduce the TDS in water include:

  • carbon filtration
  • reverse osmosis (RO)
  • distillation
  • deionization (DI)

Call us at 760.734.5787 and get in touch with one of our water experts today!


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