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5 Things Not Commonly Known About TDS in Water



TDS stands for total dissolved solids. Like the name suggests, TDS testers allow users to evaluate the amount of ionized solids dissolved in a liquid or solution without going through the trouble of evaporating the liquid and weighing the residual elements. H2O has a TDS value of zero—in other words, there are no dissolved elements in pure water that have an electrical charge. Because ionized solids will boost the electrical conductivity (EC) of water, the amount of TDS is gauged using an electrical current that measures EC levels.

There are many misconceptions about TDS testers and about TDS in general. We’ve outlined five lesser-known facts about TDS in water.

1. TDS can be healthy or unhealthy.

When many people think of TDS, they think of water contaminants, such as sewage and runoff. But TDS is not universally safe or unsafe in nature. The U.S. Environmental Protection Agency (EPA) stipulates the maximum level of TDS allowed in safe drinking water as 500 parts per million (ppm). That said, just because a water sample has a TDS value below 500 ppm, that doesn’t mean it’s safe to consume.

Although TDS testers can gauge the amount of elements dissolved in water, TDS testing alone cannot identify what those elements are. For this reason, TDS testing often serves as part of a more robust water-quality monitoring strategy that checks for other factors as well, including temperature, conductivity, salinity, and pH.

2. Not all TDS testers are created equal.

Although any element that’s dissolved in water will have an electrical charge, not all TDS testers are engineered to account for elements that are poor conductors. Elements such as oils and some pharmaceutical chemicals can be poor electrical conductors. If your TDS tester isn’t capable of detecting very low EC, it’s possible you’re not seeing the full picture. Before interpreting TDS readings as “safe,” make sure to look into the EC sensitivity of your tester.

3. TDS testers can be used to identify hard water.

If you’ve ever used hard water—water with elevated levels of minerals, typically magnesium and calcium—then you’ve experienced water with an elevated TDS level. Significantly hard water leaves hard, crusty mineral deposits in drains, showers, sinks, toilets, and more. It can have an unpalatable taste, cause skin irritation and dryness, erode pipes and water-dependent appliances, clog drains, and make it more difficult to clean clothes. TDS testers can measure the “hardness” or “softness” of water and help homeowners plan accordingly.

4. TDS testing has many applications.

Articles on TDS testers tend to focus on their benefits and pitfalls as water safety detectors, but this is just one application. Measuring TDS can be an important part of scientific, medical, and environmental research and has applications in aquaculture, renewable energy research, hydraulic fracking, food and beverage production, and many other fields.

5. High organic TDS levels are responsible for creating limestone around hot springs.

If you’ve been to Mammoth Hot Springs in Yellowstone National Park, then you’ve witnessed the natural effects produced by specific dissolved solids in water. The yellowish, rusty-colored limestone that gives the national park its name is the result of extremely high levels of organic TDS. As hot water is forced upward to the earth’s surface, it forms a carbonic acid, which dissolves limestone layers deep within the earth’s crust. When the hot spring water eventually comes in contact with air, the CO2 is released and the dissolved limestone is transformed back into a solid mineral deposit.

For more information about how to interpret TDS readings and use TDS testers, be sure to research your chosen tester’s unique features and applications. To shop Jenco Instruments’ variety of water-quality monitors with TDS testing capabilities,  click the button below.

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