Total Dissolved Solids (TDS): What is TDS in water?
Total Dissolved Solids – also known as “TDS” – is terminology often used in water filtration, especially in regards to Reverse Osmosis. In this article, we’ll look at what is TDS in water, how to measure it, and what it all means. There are also some misconceptions surrounding TDS in water so we’ll also clear those up too.
Jump to:
- What is TDS in water?
- How much TDS is good for drinking water?
- How to measure TDS
- How to reduce TDS in water
- Misconceptions about TDS
What is TDS in water?
All natural water contains minerals and dissolved substances. Total dissolved solids (TDS) are the concentration of these minerals and dissolved substances in water. TDS is mainly naturally occurring minerals and inorganic salts such as calcium, magnesium, potassium, sodium, carbonates, nitrates, bicarbonates, chlorides and sulfates.
TDS can come from quite a few sources including natural ones and as a result of human activities. For example, spring water may have high levels of dissolved solids because it flows through a region where the rocks have a high salt content. Or, in some areas like the prairies of North America there may be high levels of dissolved solids due to high amounts of calcium and magnesium in the ground.
In terms of human activities, agriculture runoff and wastewater discharges can carry excess minerals into water sources. The salt used to de-ice roads can also impact water sources.
How much TDS is good for drinking water?
Determining whether TDS in water is a good thing or a bad thing depends on the level of dissolved solids in water. Minerals in drinking water are beneficial to your health but when too much or too little of them are present, it’s not ideal. The perfect amount of TDS in drinking water is 300 – 500 ppm. Although the EPA does not federally enforce the guideline, they suggest that community water systems should contain 500 mg/L (500 ppm) or less of total dissolved solids.
- Low TDS (: missing some or all of the minerals that are beneficial to your health
- Excellent TDS (300 – 500 ppm): sweet spot for TDS in drinking water
- Fair TDS (500 – 1,000 ppm): consider an appropriate filtration system to lower your TDS
- Poor TDS (1,000 – 1,999 ppm): not recommended or safe, use an appropriate filtration system to lower your TDS
- Unacceptable TDS (> 2,000 ppm): Any TDS level above 2000 ppm is wholly unsafe; household filters can not handle this level of contamination
How to measure TDS
A TDS meter will measure for total dissolved solids. Some reverse osmosis systems even have a TDS meter built in to monitor the levels.
If your water comes from a municipal source, you can a request a water report from your water provider which will include the TDS level of your water. Keep in mind that the report will not explain reasons for high TDS that are specific to your house (i.e., corroded pipes).
Total dissolved solids (TDS) is measured as a volume of water: milligrams per liter (mg/L) or parts per million (ppm) which are one-in-the-same.
How to reduce TDS in water
Reverse osmosis is the most comprehensive and popular way to reduce TDS in water. Reverse osmosis eliminates virtually all TDS, or at least should reduce it to a very low level (
Keep in mind, a TDS reading does not indicate which dissolved solids are present. TDS is most likely minerals, but if you have an issue like odor or spots on your fixtures, you should investigate further to see what type of substance is causing the problem. A home water test kit can help with this. Ultimately, the more you know about the makeup of your water, the better you can identify a water filtration system to solve your issues.
Alternatively, you can also use a water distiller or deionization (DI) system to reduce TDS.
Ultrafiltration may reduce TDS, but ultrafiltration is not designed for TDS levels over 500 ppm nor does it actively remove or reduce TDS. One of the main benefits of ultrafiltration is that it maintains healthful minerals (TDS), so therefore it is not actively removing TDS. Any TDS reduction with ultrafiltration is by chance or due to fluctuations in TDS levels in the incoming water.
Misconceptions about TDS
” TDS is a measure of water quality. “
TDS alone is not a measure of water quality. TDS measures the level of dissolved solids in your water- it does not measure anything else. Drinking water quality should be determined based on a variety of indicators such as:
- Microorganisms – Cryptosporidium, Giardia lamblia, Legionella, Total Coliforms (including fecal coliform and E. Coli), turbidity, viruses
- Disinfectants – Bromate, Chlorite, Haloacetic acids, Total Trihalomethanes (TTHMs)
- Disinfection byproducts – Chloramines, Chlorine, Chlorine dioxide
- Inorganic chemicals – Arsenic, Asbestos, Barium, Beryllium, Cadmium, Chromium, Copper, Cyanide, Fluoride, Lead, Mercury, Nitrate, Nitrite,
- Organic chemicals – Benzene, Benzo(a)pyrene (PAHs), Carbon tetrachloride, Polychlorinated biphenyls (PCBs)
- Radionuclides – Uranium, Alpha and Beta particles
- Other contaminants / factors – pH, TDS, sediment, Iron, manganese, tannins
A comprehensive water quality report should test for microorganisms, disinfectants, disinfection byproducts, inorganic chemicals, organic chemicals, radionuclides, and more.
Reverse osmosis water is absent of anything in it – no taste, odor, and color – so testing the level of TDS in RO water can be a great way to check your reverse osmosis system is working properly, but remember a TDS meter only measures if there are dissolved solids present in the water.
” My TDS level is not close to zero…my system isn’t working. “
It’s a huge misconception that if a TDS reading is not very close to zero, their filtration system isn’t working or that it’s inefficient. You must consider what type of filtration you have!
Monitoring TDS levels is most helpful if you have a reverse osmosis system. Reverse osmosis is intended to take everything out of the water including naturally occuring minerals (TDS). You would expect to see a very low TDS level with a reverse osmosis system (
If you have an ultrafiltration system, one of the benefits of this style of filtration is that it keeps healthful minerals in your water. As a result there will be a healthy level of TDS in your water. A lot of folks make the switch from a reverse osmosis system to an ultrafiltration one and panic when the TDS reading is not close zero or close to the TDS level their RO system provided. A reverse osmosis system should be removing everything including the minerals; ultrafiltration retains healthful minerals. Remember that the perfect amount of TDS in drinking water is 300 – 500 ppm. Ultrafiltration may reduce TDS slightly if you have 500 ppm or less, but it will not remove it all. Ultrafiltration does not add minerals to water either, it maintains what’s already in there. Keep in mind that if your incoming water has more than 500 ppm TDS, ultrafiltration is not recommended.
Routine testing for TDS can provide assurance that your RO system is working like it should. If you have a reverse osmosis system, the TDS level should remain low (
If you have an ultrafiltration system, your TDS will depend on your incoming water. You can monitor TDS to check that it’s within the healthful range (up to 500 ppm), but a spike in TDS levels is not a reflection of whether the system is working as it should or not.
” Any TDS is bad. “
There’s also a misunderstanding that any TDS level except an extremely low amount is bad. Like discussed above, having some TDS in your water in beneficial to health and taste. The ideal amount of TDS in drinking water is 300 – 500 ppm. Some folks panic if their TDS level is not close to zero. There is absolutely no reason to panic from a health standpoint if your TDS is anywhere 500 ppm or lower. Low TDS also may cause your water to have a flat taste.
If you you have a reverse osmosis system you should expect to see a very low TDS level (
Some opt for reverse osmosis filtration because they prefer the taste of having virtually nothing in their water, while some prefer to keep some natural minerals in their water. High levels of TDS affects the taste of your drinking water. Depending on the type of dissolved solid, water could cause a bitter, salty, or even a sulfuric taste or odor.
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