TDS meters are a handy new way to evaluate water quality. Inexpensive, reliable and straightforward to use, these must-have digital devices measure contaminant levels in seconds. But while TDS meters offer a glimpse of what may be lurking in your cup, they don’t tell the whole story. Let’s take a closer look at their capabilities, limitations, and how they fit into your comprehensive water safety plan.
What is TDS?
TDS is a measure of solid substances dissolved in water, including minerals, metals and organic material smaller than 2 microns. Larger particles are called Total Suspended Solids (TSS). The distinction is essential when shopping for water filters according to their micron filtration rating.
Total dissolved solids are present in all untreated tap water — they occur naturally in the rock and mineral deposits found in underground aquifers and human-made sources from agricultural and road runoff to plumbing and wastewater discharge.
Are total dissolved solids safe?
The EPA regulates TDS in municipal water supplies, but they set no upper limit, only recommendations. Levels lower than 300 mg/L are excellent and reflect the presence of beneficial minerals like potassium. Water with readings between 300 – 900 mg/L is safe but may have a bitter or metallic taste. TDS level greater than 900 mg/L signal probable contamination and should be investigated.
How do TDS meters work?
TDS meters measure the electrical conductivity of water. Pure water is a poor conductor, but dissolved solids carry a distinct electrical charge that correlates directly to TDS levels. The greater the charge — the higher the level of dissolved solids. It’s the quickest way to get a feel of what in your water.
But meters are non-selective, meaning they read only total levels of dissolved solids — they don’t measure specific contaminants. They’re also not sensitive enough to detect uncharged or low-charged ions like lead, pesticides, herbicides, petroleum products and trace pharmaceuticals. If you’re worried about select toxins, it’s like knowing there are fish in your pool without knowing if you’re swimming with guppies or Great White sharks.
The bottom line is — TDS meters are a useful screening tool, but they can’t tell you if your water is safe to drink.
What You Should Know: TDS Meter Reading & Your Drinking Water
Are High TDS Readings a Reason to Filter Drinking Water?
High TDS levels are not necessarily unhealthy, but they can reflect significant water quality issues that would benefit from filtration. Hard water, for example — water with high levels of calcium and magnesium — has a bitter taste and can be unpalatable to drink. It also forms limescale deposits in plumbing that can lead to high utility bills and costly appliance repairs.
Should you purchase a TDS meter to test your tap water?
TDS meters aren’t a substitute for water testing, but they can play an important role in monitoring your home water quality.
Since most dissolved solids are likely to be minerals, gardeners benefit by knowing what they’re watering plants with. Higher TDS levels are beneficial for most flowers and vegetables. Fans of alkaline water and its many health benefits are also happy to know what they’re drinking.
Similarly, checking levels in fish tanks improves the habitat and keeps testing costs under control. TDS concentrations above 300 mg/L may reduce water clarity and decrease photosynthesis in sensitive aquatic plants. It can also contribute to irregularities in aquarium temperature and digestive problems in fish. Aquarium filters only remove Total Suspended Solids(TSS).
Once tested, aquarists can test tap water with a meter before adding it to the tank, blending it with purified water to achieve an ideal TDS balance while saving more expensive test strips only to troubleshoot specific substances. It’s a money saver.
Finally, it’s not unusual for shallow wells to become contaminated with solids in areas prone to flooding. A quick check with a TDS meter can tell you if floodwaters have infiltrated your well and further testing is required. Meanwhile, you can keep your family safe by switching to bottled.
Meters can also evaluate municipal water any time there’s an unexpected change. A water main break, for example, may cause a sharp rise in dissolved solids that can carry potentially dangerous contaminants with them.
If you can only afford a water test or a TDS meter, choose the test. But for less than $20, a meter offers enough peace of mind to be a worthwhile investment.
If you already have a TDS meter, you’re a step ahead in managing your water safety. But because older, less sensitive models detect fewer dissolved solids with low electrical charges, you’ll benefit from an upgrade to more advanced technology if your meter is more than two years old.
What do I do if my water is contaminated?
If a TDS meter suggests contamination, it’s probably safe to bathe and launder clothes with, but you should switch to bottled for drinking and cooking while you arrange a water test. Some problems, especially with municipal water, are only temporary. Other issues may require a home water filtration system.
Choosing a Water Test
Any water can be contaminated regardless of TDS levels. The only way to know with certainty is to test it — but it’s not cheap. Comprehensive testing can cost hundreds. The trick is to identify which contaminants are more likely to be present based on your water source and watershed characteristics.
Municipal supplies should be biologically safe to drink but may contain:
- Added fluoride
- Hard minerals
- Residual disinfectants such as chlorine
- Chemical by-products of disinfection, including bromate, haloacetic acids and trihalomethanes
- Emerging contaminants including pharmaceuticals, microplastics and PFAS
- Toxins that enter the water supply after they leave the treatment plants, such as lead from aging underground pipes
Do not rely on a TDS meter to detect most of these contaminants except for hard minerals.
If you have a private well, it’s your responsibility to test it. Watershed maps can narrow the scope of testing by identifying potential contamination sources near your home, such as farms, industrial centers, landfills, mining operations and more.
Wells should be tested for bacteria, hardness and other contaminants based on watershed risks. Most states suggest comprehensive testing every few years plus periodic monitoring — this is when a TDS meter is helpful because it detects unexpected changes between tests.
Water testing is available through certified laboratories nationwide — it’s a simple process — or you can purchase a reliable DIY kit online at a competitive price.
A TDS meter isn’t a substitute for a water test, but it’s one more tool that improves your ability to manage your home water quality. It’s inexpensive technology with benefits that justify its cost.