TDS, or Total Dissolved Solids, measures the amount of dissolved substances present in water. It's commonly used to understand the overall mineral and salt content of water — but TDS does not tell you whether water is hard. Water hardness is primarily caused by dissolved calcium and magnesium and needs to be measured separately.
A TDS meter is used to know if the level is good, high or safe — but the number alone does not tell the whole story. To understand your water, it helps to know what TDS measures, what the number means, and how it's different from water hardness.
What Is TDS in Water?
TDS stands for Total Dissolved Solids. It refers to the combined amount of dissolved inorganic salts and small amounts of organic matter present in water. The exact composition depends on the source of the water and the minerals or other substances it has picked up along the way.
WHO identifies calcium, magnesium, sodium, potassium, carbonate, bicarbonate, chloride, sulphate and nitrate among the principal constituents commonly found in TDS. TDS is generally expressed as milligrams per litre (mg/L) or parts per million (ppm).
What Does a TDS Reading Actually Tell You?
A TDS reading tells you how much dissolved material is present in the water. It does not tell you exactly what that material is. This distinction is important because two water samples can have a similar TDS level but contain different proportions of dissolved minerals and salts. That's also why TDS should not be treated as a complete water-quality test.
Which TDS Level of Water Is Safe for Drinking?
| Standard | Guidance |
|---|---|
| WHO | No strict health-based limit set, but considers water above 1000 mg/L unacceptable; palatability decreases above 600 mg/L |
| BIS (IS 10500) | Acceptable limit of 500 mg/L; permissible up to 2000 mg/L only where no alternative source is available |
| EPA | Secondary standard of 500 mg/L, primarily for taste and aesthetics |
| ICMR | Recommends TDS between 100–500 mg/L for good health |
What Does Research Say About TDS?
According to the World Health Organization (WHO), Total Dissolved Solids measures the combined amount of dissolved substances in water, including minerals and salts such as calcium, magnesium, sodium, potassium, chlorides and sulphates.
TDS indicates how much dissolved material is present in water, but it does not directly measure water hardness or determine whether water is safe to drink. Read the research →
Does High TDS Mean Hard Water?
No. High TDS does not necessarily mean hard water. TDS measures the total amount of dissolved material in water. Hardness refers primarily to the amount of dissolved calcium and magnesium. Calcium and magnesium contribute to TDS, but so do many other dissolved substances.
Total dissolved material
Primarily calcium + magnesium
The TDS number tells you how much dissolved material is present overall. A separate hardness test is needed to determine how much calcium and magnesium are present.
How Do You Check TDS in Water at Home?
You can check TDS at home using a TDS meter. A basic TDS check involves:
Take a Clean Water Sample
Collect the water you want to test in a clean glass or container.
Test the TDS Meter in the Water
Place the meter's probe into the water according to the manufacturer's instructions.
Read the Displayed Value
The meter will show an approximate TDS reading, usually in ppm.
Most handheld TDS meters estimate TDS from the water's electrical conductivity. WHO describes conductivity-based measurement as a common method for determining TDS.
Can a TDS Meter Measure Water Hardness?
No. A TDS meter cannot directly measure water hardness. It can tell you the total dissolved-solids level, but it cannot tell you how much of that reading comes from calcium and magnesium. If your concern is hard water, scale or mineral buildup, test hardness separately.
How Can You Reduce TDS in Water?
The right way to reduce TDS depends on what is contributing to the TDS in the first place. Reverse osmosis (RO) is designed to reduce many dissolved salts and minerals from water. Other filtration technologies target different substances and may have little effect on TDS.
| Method | What It Targets |
|---|---|
| Reverse Osmosis (RO) | Can reduce many dissolved salts and minerals, therefore lowering TDS |
| Activated Carbon Filtration | Primarily targets chlorine and certain organic compounds — not a general TDS-removal technology |
| Water Softening | Targets hardness-causing calcium and magnesium — designed to address hardness, not remove all dissolved solids |
Find the Right WaterScience Solution
TDS and hardness are two different concerns, and each needs the right kind of treatment. Whether your priority is whole-home hardness or everyday shower water quality, WaterScience has a solution built for it.
- Water softeners for whole-house hardness reduction
- Shower & tap filters for point-of-use water quality
- Solutions designed for Indian water conditions
- Choose based on what your water actually needs
Frequently Asked Questions
How much TDS should be in drinking water?
BIS IS 10500 specifies 500 mg/L as the acceptable TDS limit for drinking water in India and 2000 mg/L as the permissible limit in the absence of an alternate source.
Is 500 TDS safe for drinking water?
500 mg/L is the BIS acceptable limit for TDS in Indian drinking water, but TDS alone cannot establish overall drinking-water safety. Other chemical and microbiological parameters also need to be considered.
Is 1000 TDS safe for drinking water?
1000 mg/L is above the BIS acceptable TDS limit of 500 mg/L but below the permissible limit of 2000 mg/L that applies when no alternate source is available. TDS alone, however, cannot determine overall drinking-water safety.
Does high TDS mean hard water?
No. High TDS does not necessarily mean hard water. TDS measures total dissolved substances, while hardness is primarily associated with dissolved calcium and magnesium.
How can I reduce TDS in water?
TDS can be reduced using treatment technologies designed to remove dissolved solids, such as reverse osmosis. The appropriate treatment depends on what is contributing to the TDS and what the water is being used for.
Does RO reduce TDS?
Yes. Reverse osmosis can reduce many dissolved salts and minerals in water and therefore reduce TDS.
Does UV reduce TDS?
No. UV treatment is designed to inactivate microorganisms; it does not remove dissolved salts and minerals and therefore does not reduce TDS.
Does a water purifier reduce TDS?
It depends on the purification technology. A purifier using RO can reduce TDS, while technologies such as UV primarily address microorganisms rather than dissolved solids.
Do I need a water filter or water softener for hard water?
If the problem is hardness throughout the home, a water softener is the appropriate type of treatment to consider. A shower filter serves a different purpose and is designed for point-of-use treatment of shower water.
