If you’re researching home water purification, chances are you’ve stumbled across the term “TDS.” Don’t get lost in the jargon. We’re here to help:
What does TDS mean?
TDS stands for Total Dissolved Solids.
This is a measurement of inorganic contaminants only. It does not measure organic contaminants or biological contaminants. TDS is a measurement of substances like salts, minerals, and other solid inorganic contaminants. It is usually expressed as parts per million (ppm) but can also be expressed as parts per billion or even lower concentrations for ultra-pure water.
As noted above, TDS meters do not detect all contaminants or even all solids. Nor do they detect dissolved gases. For example, chlorine doesn’t affect the conductivity of water, so a TDS meter will not measure it. Water with a TDS of 0 can still be contaminated. It can still be contaminated with toxic gases or some biological contaminant such as bacteria, protozoa or viruses.
How do you measure TDS?
A TDS meter uses conductivity to get a baseline for how contaminated your water is.
It’s a common misconception that water is conductive. That’s why we worry about electrocution when there are appliances near the bathtub. In reality, it’s the contaminants in the water – mainly salts – that conduct electricity.
If you have ever seen or used a light bulb tester, it was demonstrating the presence or absence of the total dissolved inorganic solids in water or some other liquid, depending on how bright the light bulb is. In distilled water, the bulb shows no light at all! (Watch the video below to learn more.)
Some people wonder if TDS meters are accurate. TDS should be measured a room temperature. Some TDS meters have a built in temperature compensation, which will make the reading more accurate. Heat makes the TDS meter reading of a liquid somewhat higher. (Vice versa for cold liquids.) If battery operated TDS meters are been used, the batteries need to be at or near full power.
Is high TDS bad?
Not necessarily but it can be. It depends on what the solid components of the liquid are. Even very small amounts of some solids can be toxic.
Is low TDS good?
It can be but not necessarily. Again it depends on what organic or biological components are present. The purity or safety of a liquid should not ever be based on just the measurement of TDS. Freshly distilled water normally will have a TDS very near zero and a pH factor at or very near 7. Upon standing in an open container the pH of distilled water will drop slightly due to the dissolving of carbon dioxide from the air. The TDS will remain virtually unchanged. Pure water enthusiasts realize that no water is 100% pure, but distilled water is the most nearly pure, and that it is the most beneficial for consumption.
Should I be worried about TDS?
TDS readings can vary without necessarily being nefarious. For example, a good cup of coffee will have an elevated TDS (because coffee is dissolved in the water). But a high TDS could mean that there is something dangerous in your water too.
Testing TDS acts like a smoke detector. If it’s going off, you might’ve just burned a bit of dinner… or there might actually be a fire. The bottom line is that if you have an elevated TDS reading, then you and your family aren’t drinking pure water. There’s something in it.
What is a “Normal” TDS?
“Normal” is a subjective term. “Normal” TDS for tap water is much different than “Normal” for distilled water which is 0 – 5 ppm.
The highest TDS readings are those of ocean water. They are consistently at or near 35,000 ppm. The United States EPA has a secondary (unenforceable) standard of 500 ppm. TDS varies from area to area and even from time to time of the year. The TDS readings of ground water (especially deep well water) is more consistent. The TDS readings from river water are the least predictable. They can vary hour by hour!
Other Frequently Asked Questions About TDS
If you have any additional questions about TDS that we don’t address below, please let us know! You can email us at info@MyAquaNui.com or comment on this blog post. Thanks!
Are TDS and ppm the same?
Though there is a close relationship between TDS and Electrical Conductivity (EC), they are not the same thing. Some TDS meters are calibrated in parts per thousand. (ppt) Most of the scientific TDS meters are calibrated in mS/cm. (MicroSiemens per centimeter) For conversion from one scale to the other, 1 ppm equal 1.56 mS/cm.
Are TDS and hardness the same?
No. Hardness refers to a specific category of dissolved solids. In the water conditioning industry, hardness minerals are usually measured in grains per gallon. For conversion purposes, 1 grain per gallon of hardness is equal to 17.1 ppm of hardness minerals. (Mostly Calcium Carbonate)
How do I reduce TDS?
There are lots of ways to reduce TDS. Even a simple carbon filter can lower the total dissolved solids. However, please remember that this is only one type of contamination. TDS does not measure things like dissolved gases or bacteria.
If you want the most pure water you can get, an AquaNui distillation system is the way to go. Not only will it drastically reduce or eliminate TDS, but it will protect you from the broadest spectrum of contaminants. Learn more about why distillation systems are superior to other water purification methods.