When assessing drinking water quality, Total Dissolved Solids (TDS) is often the first number people look at. A TDS meter is inexpensive, easy to use and can provide a quick indication of the amount of dissolved material in water.

But is TDS enough to determine whether water is safe to drink?

No. Drinking water quality depends on a combination of physical, chemical and microbiological parameters. Two water samples can have similar TDS readings but very different compositions and treatment requirements.

This is why effective drinking water treatment begins with understanding the source water and identifying the contaminants that need to be controlled—not simply targeting a particular TDS value.

In India, drinking water quality is assessed against the requirements of IS 10500, which covers parameters including pH, turbidity, total dissolved solids, hardness, chloride, fluoride, nitrate, iron and microbiological quality.

What Does TDS Actually Tell You?

Total Dissolved Solids, or TDS, represents the concentration of dissolved substances in water. These can include minerals and salts such as calcium, magnesium, sodium, bicarbonates, chlorides and sulphates, along with small amounts of dissolved organic matter.

According to the World Health Organization (WHO), TDS does not have a health-based guideline value because available evidence does not establish it as a health concern at the concentrations normally found in drinking water. However, high TDS can affect the acceptability and taste of water.

Therefore, a TDS reading should be treated as one indicator of water quality—not a complete safety test.

Why a Low TDS Reading Does Not Automatically Mean Better Water

A very low TDS reading means that relatively few dissolved ions remain in the water. This can occur after processes such as reverse osmosis or demineralisation.

However, TDS does not tell you exactly which substances are present or absent. A TDS meter cannot independently confirm whether water contains microorganisms, specific heavy metals, pesticides or other contaminants.

For example, water with a low TDS reading may still require microbiological treatment if there is a risk of bacterial contamination. Similarly, water with a higher TDS reading may require investigation to determine which dissolved substances are responsible for that value.

The treatment objective should therefore be appropriate finished-water quality, rather than simply achieving the lowest possible TDS.

7 Key Parameters That Should Be Checked in Drinking Water

1. Total Dissolved Solids (TDS)

TDS provides an overall indication of the concentration of dissolved solids in water.

It is useful for monitoring changes in source-water quality and assessing the performance of processes such as reverse osmosis. However, it does not identify individual contaminants.

WHO notes that TDS can influence water acceptability and taste, but does not assign a health-based guideline value to TDS itself.

2. pH

pH indicates whether water is acidic, neutral or alkaline. It is an important parameter for drinking water because it can influence corrosion, scaling, treatment performance and the effectiveness of some treatment processes.

IS 10500 includes pH among the organoleptic and physical parameters used for drinking-water assessment.

Monitoring pH is particularly important in treated water systems where chemical dosing, filtration, disinfection or membrane processes are involved.

3. Turbidity

Turbidity describes the cloudiness of water caused by suspended particles and other materials.

High turbidity can affect the appearance and acceptability of water and may also interfere with certain treatment and disinfection processes.

For this reason, turbidity is routinely considered alongside TDS when evaluating drinking-water quality. IS 10500 lists turbidity as one of the physical parameters for drinking water.

4. Hardness

Water hardness is primarily associated with dissolved calcium and magnesium.

Hard water can contribute to scale formation in pipes, heaters, boilers and other equipment. It can also affect soap consumption and water-system performance.

Depending on the source-water characteristics and application, hardness can be managed using processes such as ion exchange, softening, membrane treatment or other suitable technologies.

5. Microbiological Quality

One of the most important differences between TDS testing and complete drinking-water testing is microbiological assessment.

A TDS meter cannot establish whether water contains disease-causing microorganisms. Drinking-water safety therefore requires appropriate microbiological controls and, where applicable, testing for organisms used as indicators of contamination.

WHO’s drinking-water guidelines use a risk-based approach that considers microbiological and chemical hazards as part of overall water safety management.

Depending on the source and treatment system, technologies such as filtration, ultrafiltration, ultraviolet treatment, ozonation, chlorination or other disinfection methods may be incorporated into a water-treatment system.

6. Specific Chemical Contaminants

TDS provides an aggregate measurement and does not identify individual dissolved substances. This is why specific chemical parameters may need to be tested according to the source of water and the potential contamination risks.

Depending on the location and source, relevant parameters can include:

• Fluoride
• Nitrate
• Iron
• Manganese
• Chloride
• Sulphate
• Arsenic
• Lead and other metals
• Ammonia
• Other source-specific contaminants

IS 10500 covers a broad range of chemical parameters in addition to TDS, demonstrating why a single TDS measurement cannot replace comprehensive water-quality assessment.

7. Taste, Odour and Colour

Water can meet certain numerical parameters and still have undesirable taste, odour or appearance.

These characteristics are therefore also considered in drinking-water assessment. IS 10500 includes colour, odour and taste among the organoleptic and physical parameters for drinking water.

Changes in taste, smell or colour can also be useful warning signs that warrant further investigation of the source water or treatment system.

TDS vs Complete Water Quality Assessment

Parameter	What It Indicates	Why It Matters
TDS	Overall dissolved solids	Useful for monitoring dissolved mineral and salt levels
pH	Acidity or alkalinity	Important for water chemistry and treatment performance
Turbidity	Cloudiness or suspended particles	Important for appearance and treatment performance
Hardness	Calcium and magnesium content	Relevant to scaling and water-system performance
Microbiological parameters	Microbial contamination	Essential for assessing biological safety
Specific chemicals	Individual contaminants	Important when source-water contamination is possible
Taste, odour & colour	Organoleptic characteristics	Important for consumer acceptability and detecting changes

How Water Source Affects Treatment Requirements

There is no single treatment process that is appropriate for every water source.

Groundwater, surface water, municipal water, borewell water and other sources can have significantly different characteristics. The treatment system should therefore be designed after understanding the raw-water quality and the required finished-water specification.

For example:

• High hardness: may require softening or ion exchange.
• High TDS: may require membrane-based treatment such as reverse osmosis, depending on the composition of the dissolved solids.
• Microbiological contamination: may require appropriate filtration and disinfection.
• Iron or manganese: may require specialised removal processes.
• Arsenic or other specific contaminants: may require targeted treatment technology.
• High turbidity: may require clarification, coagulation or filtration before downstream treatment.

Mapril’s drinking-water treatment solutions combine technologies including reverse osmosis, ultrafiltration, electrochlorination, ozonation and resin-based treatment, depending on the characteristics of the water and the required application.

Why Water Testing Should Come Before Treatment Selection

Choosing a water-treatment system based only on a TDS reading can result in an inappropriate treatment approach.

A proper water analysis helps identify:

• The major dissolved constituents
• Hardness and alkalinity
• Potential heavy-metal contamination
• Microbiological risks
• Turbidity and suspended matter
• pH and other relevant chemical parameters
• The overall treatment requirements

Once the water profile is understood, treatment technologies can be selected according to the actual contaminants and the desired quality of the treated water.

How Ion Exchange Technology Can Support Water Treatment

Ion exchange is one of the technologies used to selectively remove or exchange dissolved ions from water.

Ion exchange resins can be designed for specific treatment objectives, including hardness reduction and the removal of selected dissolved contaminants. Mapril’s portfolio includes ion exchange resin solutions for water-treatment applications, including potable-water treatment and specialised contaminant removal.

For drinking-water applications, ion exchange may form part of a larger treatment train rather than functioning as a standalone solution. The appropriate configuration depends on the source-water chemistry, target contaminants, required water quality and operating conditions.

What Is the Right Way to Judge Drinking Water Quality?

Instead of asking only, “What is the TDS of the water?”, a more useful approach is to ask:

• What is the source of the water?
• What contaminants are present?
• What does the complete water analysis show?
• Does the treated water meet the applicable drinking-water requirements?
• Is the treatment system adequately maintained?
• Is the water protected from contamination after treatment?

This approach is consistent with modern drinking-water safety management, where water quality is evaluated through multiple parameters and risks rather than relying on one measurement. WHO’s current drinking-water guidance emphasises comprehensive, risk-based management from the water source through to the consumer.

Conclusion: Look Beyond the TDS Number

TDS is a useful water-quality indicator, but it should not be treated as a standalone measure of drinking-water safety.

A complete assessment considers TDS, pH, turbidity, hardness, microbiological quality, specific chemical contaminants and organoleptic characteristics. The right treatment technology should then be selected according to the source-water profile and the required finished-water quality.

For homeowners, institutions and industries alike, the goal should not simply be to achieve a particular TDS number. The goal should be to produce water that meets the applicable quality requirements consistently and reliably.

Mapril provides water-treatment technologies and solutions designed around different water-quality challenges. From membrane-based processes and filtration to ion exchange and disinfection technologies, the appropriate solution begins with understanding the water itself.