How Much TDS Is Safe in Drinking Water? Understanding Total Dissolved Solids

Total dissolved solids, commonly called TDS, measure the combined amount of dissolved minerals, salts, metals, and other charged substances in water.

A TDS reading can be useful for understanding general mineral content and tracking changes in water quality. However, it does not identify the individual substances in the water and should not be treated as a complete water safety test.

Water with a relatively high TDS reading may simply contain naturally occurring calcium and magnesium. At the same time, water with a low TDS reading can still contain substances that a basic handheld meter does not detect.

This guide explains what TDS means, what level is generally considered acceptable, how TDS is measured, and why additional testing may be necessary when evaluating drinking water.

What Is TDS?

TDS stands for total dissolved solids. It refers to substances that have dissolved in water and are small enough to pass through a standard filter used in laboratory TDS measurements.

Common dissolved solids can include:

• Calcium
• Magnesium
• Potassium
• Sodium
• Carbonates
• Bicarbonates
• Chlorides
• Sulfates
• Nitrates
• Silica
• Trace metals

Some dissolved solids occur naturally as water moves through rocks and soil. Others may enter water through road salt, agricultural runoff, water treatment, industrial activity, wastewater, or household plumbing.

How Is TDS Measured?

TDS is generally reported in milligrams per liter (mg/L) or parts per million (ppm). For ordinary drinking-water measurements, 1 mg/L is approximately equal to 1 ppm.

A laboratory can measure TDS by evaporating a filtered water sample and weighing the residue. Most inexpensive handheld TDS meters use a different method: they estimate TDS by measuring electrical conductivity.

Dissolved ions allow water to conduct electricity. The meter measures that conductivity and applies a conversion factor to estimate the TDS level.

For this reason, a handheld TDS meter is useful as a screening and comparison tool, but its reading is an estimate rather than a detailed chemical analysis.

What Is an Acceptable TDS Level in Drinking Water?

The U.S. Environmental Protection Agency sets the TDS limit at 500 mg/L under its National Secondary Drinking Water Regulations.

This is a secondary guideline rather than a federal health-based maximum contaminant level. Secondary standards primarily address qualities such as:

• Salty or mineral-heavy taste
• Hardness
• Mineral deposits
• Scaling
• Staining
• Discoloration

A reading above 500 ppm does not automatically prove that water is hazardous. It indicates that the water contains a relatively high concentration of dissolved material and that further testing may be appropriate to determine which substances they are.

General TDS Reading Guide

The following ranges can help consumers interpret a TDS meter, but they should not be viewed as health classifications.

Does High TDS Mean Water Is Unsafe?

Not necessarily. A high TDS reading tells you that the water contains more dissolved material, but it does not reveal whether that material consists primarily of ordinary minerals or substances that require treatment.

For example, calcium and magnesium can raise TDS and contribute to hard water. Sodium and chloride can raise TDS and create a salty taste. Nitrates, arsenic, or certain metals may also contribute to the reading, but a TDS meter cannot distinguish among them.

Two water samples can have identical TDS readings while containing very different substances.

If your water has an unexpectedly high TDS level, the most useful next step is a laboratory analysis rather than relying on the meter alone.

Does Low TDS Mean Water Is Better?

No. A low TDS reading only means that the water contains fewer dissolved ions. It does not prove that the water is free of all unwanted substances.

Many contaminants can be present at concentrations too low to cause a meaningful change in electrical conductivity. Others are not ionic and may not register on a basic TDS meter at all.

Very low-mineral water may also taste flat because calcium, magnesium, and bicarbonates contribute to the taste many people associate with fresh drinking water.

What a TDS Meter Cannot Tell You

A handheld TDS meter cannot identify the individual substances in your water. It also cannot confirm whether a particular contaminant has been reduced by a filter.

A TDS meter does not reliably test for:

• Lead
• Arsenic
• PFAS
• Chlorine or chloramine
• Volatile organic compounds
• Pesticides
• Pharmaceutical residues
• Specific biological contaminants

For information about individual substances, review your water supplier’s Consumer Confidence Report or use a qualified laboratory that tests for your specific concerns.

Our Ultimate Drinking Water Contaminants Reference Guide explains many common substances that may be found in household water.

Where Do Total Dissolved Solids Come From?

TDS can come from both natural and human-made sources.

Natural Sources

• Minerals dissolving from rock and soil
• Groundwater moving through mineral deposits
• Saltwater intrusion in coastal areas
• Natural springs and aquifers

Human-Made Sources

• Road salt runoff
• Agricultural fertilizers
• Urban stormwater
• Industrial discharge
• Wastewater
• Mining activity
• Water treatment chemicals
• Corrosion or leaching from plumbing

Because geology, climate, infrastructure, and land use differ by location, TDS readings can vary considerably between neighboring communities.

Why Measure TDS?

A TDS meter can be helpful for several practical purposes:

• Estimating overall dissolved-mineral content
• Tracking changes in a water supply over time
• Monitoring the performance of a reverse-osmosis membrane
• Comparing tap water with distilled or reverse osmosis water
• Investigating possible hardness or scaling
• Identifying an unexpected change that may justify laboratory testing

TDS is best treated as one water-quality indicator rather than a complete evaluation.

TDS and the Taste of Water

Dissolved minerals and salts can significantly affect taste.

• Higher sodium and chloride may create a salty taste.
• Iron or copper may contribute to a metallic taste.
• Calcium and magnesium may create a stronger mineral character.
• Very low-TDS water may taste flat or empty.

Individual preferences vary, and pleasant-tasting water is not necessarily free from contaminants. Likewise, mineral-tasting water is not necessarily unsuitable for drinking.

TDS and Hard Water

TDS and hardness are related, but they are not the same measurement.

Water hardness is primarily determined by calcium and magnesium. TDS includes calcium and magnesium along with many other dissolved substances.

If your water has a high TDS reading and you also notice white deposits, spots on glassware, reduced soap lather, or scale in kettles and appliances, hardness may be contributing to the result.

Learn more in our guide to what causes hard water and why most water filters do not remove it.

TDS and pH

TDS and pH measure different water characteristics.

• TDS estimates the concentration of dissolved solids.
• pH measures how acidic or alkaline the water is.
• Hardness measures primarily calcium and magnesium.
• Alkalinity measures the water’s ability to neutralize acids.

These measurements can influence one another, but none of them replaces the others. A comprehensive water analysis may include all four.

How Can TDS Be Reduced?

If your specific goal is to lower total dissolved solids, you need a treatment method designed to remove dissolved ions and minerals.

Reverse Osmosis

Reverse osmosis uses pressure to move water through a semi-permeable membrane. It is one of the most common residential methods for reducing TDS.

RO systems can substantially lower dissolved mineral content, although they require membrane maintenance, usually produce a wastewater stream, and may require a storage tank.

Distillation

Distillation heats water until it becomes steam and then condenses the steam back into liquid. Many dissolved solids remain in the original boiling chamber.

Distillation can effectively reduce TDS, but it is relatively slow and energy-intensive.

Deionization

Deionization uses specialized ion-exchange resins to remove charged ions. It is frequently used in laboratories, manufacturing, aquariums, and other technical applications.

Deionization is not usually the first choice for ordinary household drinking water because the resin must be carefully maintained and the process does not remove all types of contaminants.

Do Activated-Carbon Filters Reduce TDS?

Activated-carbon filters are commonly used to improve taste and odor and to reduce certain chemicals, depending on the filter design and performance testing.

However, activated carbon generally does not remove ordinary dissolved minerals such as calcium, magnesium, sodium, and potassium as effectively as reverse osmosis, distillation, or deionization.

As a result, a carbon-based filter may reduce certain unwanted substances without significantly affecting the TDS reading.

Berkey Water Filters and TDS

Berkey systems are countertop, gravity-fed water filtration systems that operate without electricity or a plumbing connection.

Berkey filter elements are not designed to remove all dissolved beneficial minerals from the water. Therefore, a handheld TDS meter may display a similar reading before and after filtration.

This does not automatically mean that the filter is not operating correctly. TDS is not an appropriate measurement for evaluating the reduction of substances that do not significantly affect electrical conductivity.

For example, reducing a substance to parts per billion may have little or no visible effect on a TDS reading in parts per million.

When evaluating Berkey filtration performance:

• Review the performance information for the specific filter elements installed.
• Prime and install the elements according to the instructions.
• Check that washers and wing nuts are properly positioned.
• Perform the recommended assembly checks.
• Replace the elements according to their rated capacity and condition.
• Use laboratory testing when confirmation of a specific contaminant is needed.

Compare Berkey replacement filters and their intended uses before selecting an element for your system.

Popular Berkey Water Filter Systems

Shop Berkey Water Filter Systems

When Should You Order a Laboratory Water Test?

Consider more complete testing if:

• Your TDS exceeds 500 ppm, and you do not know the cause.
• Your water suddenly changes in taste, odor, appearance, or TDS.
• The water tastes unusually salty, bitter, or metallic.
• You use a private well.
• You live near agriculture, mining, industry, airports, military facilities, or landfills.
• You are concerned about lead, arsenic, nitrates, PFAS, VOCs, pesticides, or other specific contaminants.
• A household member has been advised to limit sodium or particular minerals.

A laboratory report can identify individual substances and their concentrations, providing much more useful information than a TDS number alone.

Frequently Asked Questions About TDS

Is 500 ppm TDS unsafe?

Not automatically. The EPA’s 500 mg/L level is a secondary guideline related primarily to taste, staining, deposits, hardness, and similar effects. Water above that level should be tested to determine which dissolved substances are causing the reading.

Is zero-TDS water the healthiest water?

Not necessarily. Zero or near-zero TDS usually indicates that nearly all dissolved ions have been removed. It does not provide a complete analysis of every possible substance, and some people prefer the taste of water containing natural minerals.

Why did the TDS reading remain the same after filtration?

Many filters are not designed to remove dissolved minerals. They may reduce other substances without significantly changing conductivity, so the TDS reading can remain similar.

Can a TDS meter test whether my filter removes lead or PFAS?

No. A TDS meter cannot identify lead, PFAS, arsenic, VOCs, or other individual contaminants. Compound-specific laboratory testing is required.

Can TDS tell me whether my water is hard?

A high reading may suggest mineral-rich water, but TDS does not directly measure hardness. A separate hardness test measures calcium and magnesium more accurately.

Is ppm the same as mg/L?

For ordinary drinking-water measurements, ppm and mg/L are approximately equivalent. A reading of 500 ppm is generally interpreted as approximately 500 mg/L.

Final Thoughts

So, how much TDS is acceptable in drinking water? The EPA lists 500 mg/L as a secondary guideline, primarily because higher concentrations may affect taste, hardness, deposits, staining, and other aesthetic qualities.

However, TDS measures quantity rather than identity. It tells you approximately how much dissolved material is present, but it does not explain what that material is.

A high reading may come from common minerals, while a low reading does not prove that the water is free of all unwanted substances. Use TDS as one useful clue, then review your local water report or order targeted laboratory testing when you need a more complete understanding of your water.

For additional information, visit our Ultimate Drinking Water Contaminants Reference Guide.