As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties.
Yes, you may be able to drink water with a high TDS reading, but the TDS number alone cannot tell you whether the water is safe.
TDS means total dissolved solids. It is an estimate of dissolved minerals, salts, metals, and other charged substances in water. A high reading may come from common minerals such as calcium and magnesium. It can also rise because of sodium, chloride, sulfate, or other substances.
The important question is not only how high the TDS is, but what is causing it.
In the United States, the EPA lists 500 mg/L for TDS as a secondary drinking-water standard. This standard mainly addresses taste, staining, deposits, and similar water-quality problems rather than a health-based limit.
The World Health Organization does not set a health-based guideline value for TDS because TDS itself is not considered a health concern at the levels normally found in drinking water. High concentrations can still make water unpleasant to drink and may signal that further testing is needed.
What a High TDS Reading Actually Means
TDS is usually reported in milligrams per liter (mg/L) or parts per million (ppm). For ordinary drinking water, these numbers are close enough that a meter reading of 500 ppm can generally be thought of as about 500 mg/L.
Common dissolved substances that can contribute to TDS include:
- Calcium
- Magnesium
- Sodium
- Chloride
- Bicarbonate
- Sulfate
- Iron and other metals
Some of these are common minerals found naturally in groundwater.
This is why a TDS reading should not be treated like a simple pass-or-fail drinking-water test.
Water at 600 ppm is not automatically unsafe, and water at 100 ppm is not automatically safe.
Is Water Above 500 PPM TDS Unsafe?
Not necessarily.
The EPA's 500 mg/L value for TDS is a secondary standard, not a federal health-based maximum contaminant level. High TDS can cause salty or unusual taste, mineral deposits, staining, or scaling in plumbing and appliances.
A reading above 500 ppm does, however, give you a reason to learn more about the water.
For example, a high TDS result might be caused mostly by calcium and magnesium. In another water source, a similar reading could include large amounts of sodium or chloride.
The meter cannot tell you the difference.
That makes laboratory testing much more useful when the water will be used for drinking.
Why a TDS Meter Cannot Tell You If Water Is Safe
Most handheld TDS meters do not directly count every dissolved substance in the water.
They measure how well the water conducts electricity and use that measurement to estimate TDS. Dissolved ions such as salts increase conductivity.
This makes a TDS meter useful for watching changes in water. It is not a complete drinking-water test.
A TDS meter generally cannot tell you:
- Which minerals or chemicals are present
- Whether harmful bacteria are present
- Whether nitrate is too high
- Whether arsenic or lead is present at an unsafe level
- Whether pesticides or other specific chemicals are present
- Whether the water is safe to drink
For example, water can have a fairly low TDS reading and still contain a harmful microorganism or chemical.
The reverse is also possible. Water can have relatively high TDS because it contains a large amount of naturally occurring minerals.
When High TDS Deserves More Attention
A laboratory test becomes especially important when the source is a private well, rainwater system, spring, cistern, tank, or another supply that is not routinely monitored as public drinking water.
Pay extra attention when:
- The TDS level suddenly changes.
- The water develops a salty, metallic, or unusual taste.
- You see new staining or heavy mineral deposits.
- Flooding or construction has affected the water source.
- Agricultural activity, septic systems, industry, or road salt may affect nearby groundwater.
- The water will be used for infant formula.
- You do not know what minerals or contaminants are producing the reading.
For private wells, the EPA recommends annual testing for total coliform bacteria, nitrate, TDS, and pH, along with additional contaminants that may be relevant to local conditions. The EPA recommends using a certified drinking-water laboratory.
High TDS in Well Water
Groundwater often picks up minerals as it moves through soil and rock. Because of this, well water can naturally have much more dissolved mineral content than rainwater.
High well-water TDS can be associated with substances such as calcium, magnesium, sodium, chloride, or sulfate. Nearby land use can also matter.
A TDS meter cannot determine which of these is responsible.
If a private well has a high or rising TDS level, have the water tested for the specific substances that may be present in your area. EPA guidance also recommends considering nearby activities when deciding what to test for. Agriculture may call for nitrate testing, for example, while salty water may warrant chloride and sodium testing.
Do not choose a drinking-water treatment system until you know what needs to be removed.
High TDS in Rainwater
Rain itself normally starts with relatively little dissolved mineral material, but collected rainwater is different from rain falling through open air.
Roof runoff can contact:
- Dust
- Bird and animal waste
- Roofing materials
- Gutters and flashing
- Stored sediment
- Tank surfaces
- Plumbing components
A rainwater system may therefore have a different water-quality profile by the time the water reaches the tap.
A sudden increase in TDS can be useful as a clue that something in the system has changed. Check the roof, gutters, prefilters, tank condition, sediment buildup, plumbing, and any treatment equipment.
But low TDS does not prove collected rainwater is drinkable.
When deciding about 150 TDS drinking-water guidance, remember to verify the upkeep decision supported by reliable measurements.
Roof-collected rainwater intended for drinking should be treated as a complete water-safety system. Suitable collection, debris control, appropriate treatment, maintenance, and current laboratory testing all matter. Local drinking-water and plumbing requirements may also apply.
Can You Reduce High TDS?
Yes, but the correct treatment depends on what is dissolved in the water.
Reverse osmosis
Reverse osmosis, often called RO, uses a membrane to reject many dissolved ions. It can greatly reduce TDS when the system is suitable for the source water.
RO also produces reject water and requires filter and membrane maintenance. Its ability to remove a particular contaminant should be checked against that contaminant rather than judged only by the final TDS number.
Distillation
Distillation boils water and condenses the steam into another container. Many dissolved salts remain behind.
It can reduce TDS, but it requires energy and regular cleaning because minerals become concentrated inside the unit. Treatment performance for specific contaminants still matters.
Water softeners
A conventional ion-exchange water softener is mainly used to control hardness caused by calcium and magnesium.
It should not be treated as a general TDS-removal system. Softening changes which ions are present and may add sodium to the treated water.
Carbon filters
Activated carbon can be useful for certain tastes, odors, chlorine, and some organic chemicals, depending on the filter.
A typical carbon filter does not provide a dependable solution for high concentrations of dissolved mineral salts.
Do not choose treatment simply because a product is labeled a "water filter." First identify the actual water problem.
Should You Stop Drinking High-TDS Water?
A moderately high TDS reading by itself does not prove that water is unsafe.
At the same time, you should not assume the water is safe simply because high TDS can come from harmless minerals.
If you have an unexplained high reading from a private supply, especially one that has changed suddenly, laboratory testing is the practical next step.
If testing finds a contaminant above a health-based limit, follow guidance from your local health or drinking-water authority and choose treatment designed for that specific contaminant. EPA guidance recommends confirming contamination and seeking appropriate health guidance when a private-well test exceeds a health standard.
The Better Way to Use a TDS Meter
A TDS meter works best as a monitoring tool, not as a drinking-water safety test.
For example, you can record the normal TDS of your water and watch for large changes over time. It may also help show whether an RO system is still reducing dissolved ions as expected.
If the reading changes sharply, investigate why.
Just do not use one TDS number as proof that water is potable.
Potable means water that is suitable for drinking. Establishing that requires looking at the important microbial and chemical risks for the particular water source, not just its mineral content.
Frequently Asked Questions
Is 500 ppm TDS safe to drink?
A reading of 500 ppm does not automatically mean water is unsafe. The EPA lists 500 mg/L as a secondary standard related mainly to taste, deposits, staining, and other water-quality concerns rather than as a health-based maximum. The substances causing the TDS matter more than the number alone.
Is 1,000 ppm TDS water safe to drink?
You cannot determine safety from a 1,000 ppm TDS reading alone. Water at this level may contain large amounts of ordinary mineral salts, but the meter does not identify them. Have drinking water tested if the source or cause of the high reading is unknown.
Does low TDS mean water is safe?
No. Low-TDS water can still contain bacteria or harmful chemicals. A TDS meter is not a substitute for drinking-water testing.
Can boiling reduce TDS?
Ordinary boiling does not remove dissolved salts. As water evaporates, those salts remain behind and can become more concentrated. Distillation is different because the steam is collected and condensed separately.
Will a carbon filter lower TDS?
Usually not by much. Standard activated-carbon filters are not designed to remove most dissolved mineral salts. Treatment should be selected according to the substances actually present in the water.
Can reverse osmosis reduce TDS?
Yes. Reverse osmosis can reject many dissolved ions and normally lowers TDS substantially when properly selected and maintained. A lower reading after RO still does not replace testing for specific drinking-water hazards when those hazards are a concern.
Is high-TDS rainwater safe to drink?
Not based on the TDS reading alone. Collected rainwater can pick up microorganisms and chemicals from the roof, gutters, storage tank, and plumbing. Drinking-water use requires suitable collection and treatment along with appropriate laboratory testing.
