TDS in Drinking Water: Meaning, Levels, and Limitations

Total dissolved solids, commonly known as TDS, is one of the numbers that appears on a water report or a cheap meter that gets treated like a verdict. If the number is low, the water gets a pass, if the number is high, it begins a worry, but neither really works.

TDS is just a number that represents the total mineral, salt and other particle content dissolved in a sample of water, in parts per million.

A glass with a low reading may have something to concern about while one with a higher reading may possibly be just fine. It is useful only if the person knows what it represents and what it does not represent.

Quick Answer

Total dissolved solids (TDS) refers to the minerals, salts, and other materials dissolved in water, usually measured in parts per million. A higher reading often means salty or mineral-heavy water; a lower one can taste flat. But don't treat TDS as a report card. It's no substitute for real safety testing, which is what catches bacteria, chemicals, and metals.

Key Takeaways

• A typical TDS reading speaks to taste more than it speaks to safety.
• A basic TDS meter only catches the overall total. It won't flag specific problems like bacteria or heavy metals hiding in the mix.
• A high number by itself doesn't mean your water is unsafe to drink.
• A low number doesn't mean your water is clean either. Both readings need context.
• Only certain filtration methods, reverse osmosis being the main one, actually bring TDS down in any meaningful way.

What is TDS in Drinking Water?

TDS stands for total dissolved solids, which are anything that has dissolved into the water but is not floating around. It consists mainly of calcium, magnesium, sodium, potassium, bicarbonates, chlorides and sulfates as per the water source. TDS is not an identity, it is a quantity, it's a number that indicates approximately how much is dissolved, but not what any of it is.

What is a TDS Reading?

A TDS number is actually an average of all the natural minerals, salts and other possible things that may have become a part of the sample during the supply chain. Most handheld meters don't measure this directly but rather the conductivity of the water, as the ions within the water carry current, and estimate the total from this.

The reason TDS is measured in parts per million (ppm)

Milligrams per liter is approximately equal to parts per million (ppm). If the reading is 300 ppm, the water contains approximately 300 mg per liter of dissolved material. This is to compare water sources or to determine if your filter is working.

Different TDS Levels Actually Mean

Beyond taste and mineral content, TDS numbers don't tell you much. WHO notes water under 600 mg/L generally tastes fine, with palatability dropping past 1200 mg/L, but sets no health guideline since the number can't identify which substances are involved. EPA's 500 mg/L standard follows the same logic, addressing taste, not health.

Low TDS and High TDS Of Drinking Water

Low TDS drinking water will have a lighter taste that may be too light, as very low readings can sound like a flat taste.

High TDS goes the other way, too salty, bitter or highly mineralized, and this can lead to a build-up of scale over time in kettles and appliances.

That doesn't say if the substance dissolved is safe or unsafe. Two samples may have the same number and yet they may be chemically completely different.

Does a High TDS Number Mean Water Is Unsafe?

Not on its own. A lot of high readings simply reflect minerals naturally present in the local supply, though an unusually high number is still worth a second look against your local water quality report. Lab testing is the way to actually find out if something specific concerns you.

Does a Low TDS Number Mean Water Is Safe?

No, and this trips up more people than you'd think. Certain contaminants can be sitting in your water without moving the TDS reading at all.

Microorganisms and organic chemicals aren't something a basic meter can reliably detect, so seeing 50 ppm on the screen doesn't mean your water is free from harmful substances.

What TDS Doesn't Tell You About Water Quality

A TDS reading measures dissolved solids, nothing more. It won't catch bacteria, viruses, lead, or pesticides, and it says nothing about pH, chlorine, or hardness. Your water can look fine on a TDS meter while still having real problems.

How TDS Changes After Water Filtration

Not all water filter systems are created equal when it comes to TDS. Activated carbon filters will adsorb chlorine taste and some chemicals, leaving the dissolved minerals unchanged.

The reverse osmosis process forces water to pass through a membrane which is not large enough to allow most of the dissolved solids to pass through; the distillation process results in a similar outcome by evaporating water.

Water filters for drinking water can be tested before and after to verify that they are helping to reduce the level of TDS but a lower TDS doesn't necessarily imply that all contaminants are being removed.

What a Water Filter for 5 Gallon Jug Can and Cannot Do

A water filter for a 5-gallon jug is convenient: fill it, filter it, done. Most units target sediment, chlorine, taste, and odor, not dissolved minerals.

To actually lower TDS, skip generic purifiers and choose a water filter for 5 gallon jug built specifically for dissolved solids reduction.

When Is Water Filtration Necessary?

Filters are relevant when the water is to be used for better tasting water, for removal of known contaminants or simply for convenience. Select a water filter system that is appropriate for the actual issue, not one that is selected to obtain a lower number.

When Should You Consider Filtering Your Drinking Water?

Filtering makes sense for better tasting water, cutting down known contaminants, or just for convenience. Pick a water filter system that matches the actual problem, not one chosen to chase a lower number.

How to Read a TDS Meter without Misinterpreting the Number

Think of a TDS meter as a comparison tool rather than a full safety test. Keep it clean, follow the calibration instructions that come with it, and test samples under similar conditions each time, measuring both your source water and treated water with the same device for consistency.

Common Mistakes People Make When Using TDS as a Water Quality Test

• Chasing the lowest possible TDS number, treating it as a health goal it was never designed to measure
• Assuming 500 ppm is a hard safety limit, when it's actually an EPA aesthetic guideline, not a health threshold (the WHO sets no limit at all)
• Relying on a TDS meter to catch every contaminant, when it can't detect bacteria, chemicals, or metals
• Switching between meters without recalibrating first, since even small calibration differences between devices can throw off the numbers and lead to the wrong conclusion

Conclusion

High readings will impact flavor and lead to mineral deposits, but low readings do not exclude the possibility of contaminants not detected by conductivity testing. Understand what's in your water, identify the issue, and match your filter to the problem.

For regular drinking, a water filter for a 5-gallon jug is suitable if the filtration method is appropriate. Filtering for something other than drinking?

Check out this guide to water filter for gardening, built for that exact use.

 

Frequently Asked Questions

 

What is a good TDS level for drinking water?

The WHO states that somewhere about 600 mg per liter is best tasting, but this is a taste, not a safety limit.

Does high TDS in drinking water mean it is unhealthy?

Not necessarily. It may drive flavor to salty or mineral and contribute to deposits; if it does, it depends on the cause.

Does a TDS meter indicate if the water is potable?

No. It does not determine if any of it is harmful or not as it only measures the amount dissolved, so it does not provide a biological risk assurance about your water.

What is the significance of 500 ppm TDS in drinking water?

About 500 mg of the substance per liter, but with no indication of what it is.

Should I use a TDS meter before and after filtration?

A good test to determine if your filter is working or not, but don't take this as proof that all contaminants have been removed.