What Are Total Dissolved Solids (TDS) in Drinking Water?

If you've ever tested your water and seen a "TDS" reading, you might have wondered what it actually means. Total Dissolved Solids (TDS) is a measure of all the dissolved substances in your water. Everything from minerals and salts to metals and organic matter. While some dissolved solids are beneficial, high or low TDS levels can affect taste, appliance lifespan, and even water filtration performance.

In this guide, we’ll explore what TDS is, why it matters, how to measure it, and what to do if your levels are off. Whether you're a homeowner, coffee shop owner, or water quality enthusiast, understanding TDS can help you make smarter decisions about your water.

Defining Total Dissolved Solids

TDS refers to the total concentration of dissolved substances in water. These include:

• Inorganic salts (calcium, magnesium, sodium, potassium, bicarbonates, chlorides, sulfates)

• Metals (iron, copper, zinc)

• Organic matter (natural decaying materials, industrial runoff)

TDS is typically measured in parts per million (ppm) or milligrams per liter (mg/L). These units are functionally equivalent: 1 ppm = 1 mg/L.

Water with higher TDS levels often originates from groundwater sources that absorb minerals from soil and rock, while lower TDS water tends to come from rainwater or reverse osmosis systems.

How TDS Affects Water Quality

TDS levels influence more than just technical readings. They can affect everyday use and comfort:

• Taste and Odor: Water with low TDS (<50 ppm) may taste flat, while high TDS (>500 ppm) can have a salty, bitter, or metallic taste.

• Scaling: High levels of calcium and magnesium (contributing to TDS) cause scale buildup in kettles, pipes, and appliances.

• Appliance Efficiency: Coffee makers, water heaters, and dishwashers perform better and last longer with balanced TDS.

• Skin and Hair Effects: Excess minerals can dry out your skin or leave residues after showering.

That said, TDS is not a direct indicator of water safety. It simply reflects the total amount of dissolved material, not what those materials are.

Ideal TDS Levels for Drinking Water

The U.S. EPA sets a secondary (non-enforceable) standard for TDS at 500 ppm. That means water with more than 500 ppm isn’t considered unsafe, but it may be less palatable or cause other issues.

Here’s a general guide to TDS levels in drinking water:

Certain specialty uses (like aquariums or hydroponics) require even more precise TDS management.

TDS Meter Explanation: How It Works

A TDS meter measures the electrical conductivity (EC) of water. Because dissolved salts and minerals conduct electricity, EC readings can be converted into approximate TDS values.

How to use a TDS meter:

1. Remove the protective cap.

2. Turn the device on.

3. Dip the probe into a glass of water (not touching the sides).

4. Wait for the reading to stabilize.

5. Read the value in ppm or mg/L.

For more advanced needs, dual-probe TDS meters measure both inlet and outlet TDS, helping you track the effectiveness of filtration systems like reverse osmosis.

Featured Product: HM Digital DM-2 Commercial Dual Monitor

A great example of an advanced TDS measuring device is the HM Digital DM-2 Commercial Dual Monitor.

Product Highlights:

• Monitors inlet and outlet TDS levels simultaneously

• Suitable for commercial RO systems, hydroponics, or beverage setups

• Displays in ppm or EC units

• User-calibrated for accuracy

• Includes sensor cables and mounting bracket

This monitor helps you track your system’s performance over time, ensuring water purity without guesswork.

TDS vs. Contaminants: What It Does and Doesn’t Measure

One of the most common misunderstandings is equating TDS with water purity. TDS doesn’t tell you what's in the water, just how much is dissolved.

For example:

• Safe water may have high TDS if it includes calcium and magnesium.

• Unsafe water may have low TDS but include lead, pesticides, or bacteria (which aren’t charged particles and don’t affect conductivity).

TDS meters are great for tracking performance, like seeing if an RO system is effectively reducing mineral content, but they shouldn’t replace contaminant-specific testing.

How to Reduce or Control TDS

If your water has a high TDS level and it's affecting taste or appliances, you can reduce it using one of these technologies:

1. Reverse Osmosis (RO)

• Removes 90–99% of TDS

• Ideal for homes, aquariums, and labs

• Includes multiple stages: sediment, carbon, membrane

2. Distillation

• Boils water and collects condensed steam

• Effective but slow and energy-intensive

3. Deionization (DI)

• Uses ion exchange resins to remove charged particles

• Often used after RO for near-zero TDS

Some users intentionally blend RO water with tap to remineralize it, aiming for a mid-range TDS that balances taste and appliance compatibility.

TDS in Different Water Sources

TDS levels can vary significantly based on the source:

Municipal Water:

• Treated but may contain added minerals or chemicals

• Usually 100–500 ppm

Well Water:

• Often higher in TDS due to natural mineral leaching

• May exceed 1000 ppm in limestone-heavy regions

Bottled Water:

• Ranges from <10 ppm (distilled) to >300 ppm (mineral water)

• Check the label or test it yourself if unsure

Rainwater:

• Naturally low in TDS, often under 30 ppm

• Can be acidic or lack essential minerals

Conclusion

Understanding total dissolved solids is essential for managing water quality in homes, businesses, and specialised applications. TDS gives you a quick, general picture of how much is dissolved in your water, but it’s just one part of the puzzle.

Using tools like the HM Digital DM-2 Commercial Dual Monitor, you can keep tabs on your system’s performance and water purity. If your TDS is too high or too low, consider adjusting your filtration setup with RO or DI systems.

To explore more water quality tools and filtration solutions, visit WaterFilters.NET and take the next step toward clean, balanced water tailored to your needs.