Minimum TDS Value of Drinking Water: What Is the Ideal Level?
Understanding the minimum TDS value of drinking water is important for households, commercial facilities, water treatment companies, and industrial water users. Total dissolved solids (TDS) indicate the concentration of dissolved substances in water, including minerals and salts such as calcium, magnesium, sodium, bicarbonates, chlorides, and sulfates.
However, a low TDS value does not automatically mean that water is safe to drink. Similarly, water with a relatively high TDS value is not necessarily unsafe because the actual composition of dissolved substances also matters.
For businesses planning to install a drinking water purification system, understanding TDS levels helps determine the appropriate treatment process and equipment configuration.
This article explains the minimum TDS value of drinking water, recommended TDS ranges, relevant water quality standards, and the role of reverse osmosis technology in drinking water treatment.
1. What Is the Minimum TDS Value of Drinking Water?
There is no universally established minimum TDS value of drinking water that applies to every country and every drinking water application.
The World Health Organization (WHO) does not establish a health-based guideline value for total dissolved solids because the available evidence does not support a specific TDS concentration as a universal threshold for health effects. Instead, TDS is primarily considered in relation to water acceptability, taste, and other water quality characteristics.
Source: WHO – Total Dissolved Solids
For practical reference, the following table illustrates common TDS ranges and their general characteristics.
These ranges are general reference categories, not universal drinking water safety classifications or regulatory limits.
For water treatment projects, the appropriate TDS target depends on the raw water composition, intended use, applicable local regulations, and the requirements of the end user.
Therefore, rather than pursuing the lowest possible TDS value, water treatment engineers should establish a suitable target based on comprehensive water quality testing.
2. What Is the Ideal TDS Level for Drinking Water?
The ideal TDS level for drinking water depends on the source of the water and the preferences and requirements of the users.
Two important references help explain how TDS should be interpreted.
WHO Recommendations
WHO publications indicate that drinking water with TDS below approximately 600 mg/L is generally considered to have good palatability. At concentrations above approximately 1,000 mg/L, water becomes increasingly likely to have an unacceptable taste.
WHO does not specify a health-based minimum TDS requirement for drinking water.
Source: WHO – Guidelines for Drinking-Water Quality
US EPA Secondary Drinking Water Standard
The US Environmental Protection Agency (EPA) lists 500 mg/L as its secondary standard for TDS.
This standard addresses aesthetic and operational concerns, including taste, deposits, and other effects. It is a secondary standard rather than a federally enforceable primary health-based limit.
Source: US EPA – Drinking Water Regulations and Contaminants
These references should not be interpreted as establishing a single ideal TDS value for all drinking water.
For commercial drinking water production, bottled water facilities, hotels, and other water supply projects, the target should be determined by considering local standards, the intended application, and the complete water quality profile.
3. Why Is TDS Important in Drinking Water?
TDS is a useful water quality indicator because it helps identify the overall concentration of dissolved substances. However, it does not identify individual contaminants or determine whether water is microbiologically safe.
Several factors explain why TDS should be monitored.
3.1 Water Taste
Dissolved minerals and salts can affect the taste of drinking water.
Water with moderate mineral content may have a more noticeable mineral taste, while water with extremely low TDS may taste flat to some consumers.
For commercial drinking water suppliers, controlling TDS can help achieve a consistent product taste.
3.2 Scaling and Equipment Protection
High concentrations of certain dissolved minerals can contribute to deposits in pipes, water heaters, boilers, and other equipment.
The scaling risk depends on the individual mineral concentrations, hardness, alkalinity, temperature, and operating conditions—not TDS alone.
Industrial water treatment systems can help control dissolved salts and reduce scaling risks when properly designed for the application.
3.3 Drinking Water Treatment Performance
Monitoring TDS before and after treatment provides a practical way to evaluate the dissolved-solids reduction achieved by a reverse osmosis system.
A significant decrease in TDS can indicate that the RO membrane is removing dissolved ions effectively. However, TDS measurements alone cannot confirm that all harmful contaminants have been removed.
For this reason, drinking water quality management should include appropriate chemical and microbiological testing.
4. What Causes High or Low TDS in Drinking Water?
TDS levels vary according to the source of the water and the treatment process.
Groundwater and Well Water
Groundwater can dissolve minerals from surrounding soil and rock formations. As a result, well water may contain elevated concentrations of calcium, magnesium, sodium, chloride, and other dissolved substances.
In areas with saline groundwater or brackish water sources, conventional filtration may not sufficiently reduce dissolved salts.
An industrial reverse osmosis system may be suitable when dissolved-solids reduction is required.
Municipal Water Supply
Municipal drinking water may contain naturally occurring minerals and dissolved substances remaining after treatment.
TDS levels vary between locations because of differences in source water, geology, and treatment practices.
Seawater and Brackish Water
Seawater contains high concentrations of dissolved salts, while brackish water generally has lower salinity than seawater but higher salinity than typical freshwater.
Both sources may require membrane desalination when the objective is to produce drinking water or process water with lower dissolved-solids concentrations.
Water Treatment Processes
Different treatment technologies affect TDS in different ways.
Sand filtration: Primarily removes suspended particles and turbidity.
Activated carbon filtration: Primarily reduces selected organic compounds, chlorine, and substances affecting taste and odor.
Water softening: Reduces hardness by exchanging calcium and magnesium ions for other ions, but does not necessarily reduce overall TDS.
Reverse osmosis: Removes a substantial proportion of dissolved salts and other substances, depending on membrane characteristics and operating conditions.
EDI: Used primarily for further demineralization in suitable high-purity water applications, often after RO pretreatment.
Choosing the correct treatment process requires understanding both the raw water characteristics and the final water quality requirements.
5. How Does Reverse Osmosis Reduce TDS in Drinking Water?
Reverse osmosis is a widely used membrane separation technology for reducing dissolved salts in drinking water and industrial water treatment applications.
An RO system applies pressure to feed water and forces part of the water through a semipermeable membrane. Many dissolved ions and other substances are rejected by the membrane and discharged with the concentrated reject stream.
The resulting permeate contains substantially fewer dissolved solids than the feed water under suitable operating conditions.
Typical Industrial RO Treatment Process
A drinking water treatment system may use the following process:
Raw Water → Pretreatment → Cartridge Filter → High-Pressure Pump → RO Membrane → Post-Treatment → Disinfection → Drinking Water Storage
The actual configuration depends on the raw water quality, required production capacity, and applicable drinking water standards.
Pretreatment may include multimedia filtration, activated carbon, softening, or other processes as required. Post-treatment may include remineralization, pH adjustment, and disinfection.
For drinking water applications, the system must be designed to manage not only TDS but also microbiological risks and other relevant contaminants.
What TDS Level Can an RO System Achieve?
The final TDS concentration depends on the feed water TDS, membrane rejection rate, temperature, operating pressure, recovery rate, membrane condition, and system design.
For example, consider a system treating feed water with a TDS concentration of 500 mg/L.
If the RO system achieves an assumed 95% TDS rejection rate, the estimated permeate TDS would be:
Permeate TDS = Feed Water TDS × (1 − Rejection Rate)
500 × (1 − 0.95) = 25 mg/L
This is a simplified calculation for illustration. Actual performance must be verified through system specifications and water testing.
A low permeate TDS does not, by itself, establish that the water is safe for consumption. Additional treatment and testing may be necessary.
6. How to Choose an Industrial RO System for Drinking Water
For commercial and industrial projects, selecting an RO system requires more than specifying a target TDS value.
Xinjieyuan recommends evaluating the following factors before choosing equipment.
Raw Water Analysis
Obtain a laboratory analysis of the feed water, including TDS, hardness, alkalinity, pH, turbidity, iron, manganese, and other relevant contaminants.
Microbiological testing and additional chemical analysis may also be necessary depending on the source and intended application.
Required Water Production Capacity
Calculate the daily water demand and peak consumption.
Hotels, commercial drinking water stations, food and beverage plants, and bottled water facilities may have very different production requirements.
The RO system should be sized according to the required permeate flow rate, operating schedule, and expected recovery rate.
Required Permeate Quality
Determine the final water specifications based on local drinking water regulations and the intended application.
Some projects require moderate TDS reduction, while others may need additional purification or remineralization.
The objective should be to produce compliant, suitable drinking water rather than simply achieving the lowest possible TDS.
Pretreatment and Post-Treatment
Pretreatment protects the RO membrane from fouling, scaling, and damage.
Post-treatment may be necessary to stabilize the water, adjust taste, and provide appropriate disinfection.
For drinking water systems, sanitary storage, hygienic distribution, and ongoing water quality monitoring are also important.
Supplier Experience and Customization
When purchasing an industrial RO system, buyers should evaluate the supplier's technical support, equipment configuration, membrane selection, control system, maintenance requirements, and ability to customize the system.
Xinjieyuan provides industrial water treatment equipment and customized solutions for different feed water conditions and production requirements.
To discuss a suitable system, visit the Xinjieyuan official website.
7. How Can You Measure the TDS Value of Drinking Water?
A portable TDS meter is commonly used for quick checks of drinking water and RO system performance.
Most handheld meters estimate TDS from electrical conductivity rather than directly measuring the mass of all dissolved substances.
Follow these steps for a basic measurement:
Collect a representative water sample in a clean container.
Rinse the meter probe according to the manufacturer's instructions.
Place the probe in the sample.
Wait for the reading to stabilize.
Record the result in mg/L or ppm.
Compare feed water and treated water readings to assess the apparent TDS reduction.
For more reliable results, calibrate the instrument as recommended and use consistent sampling procedures.
Because conductivity-to-TDS conversion depends on water composition, a TDS meter should be treated as a screening and operational monitoring tool rather than a complete water quality analysis.
If the water is intended for drinking, appropriate laboratory testing should be performed to evaluate relevant chemical and microbiological parameters.
Conclusion
The minimum TDS value of drinking water is not defined by a universal health-based threshold. Instead, drinking water suitability depends on the composition of dissolved substances, applicable standards, and the results of comprehensive water quality testing.
TDS remains a useful indicator for monitoring water treatment performance, especially when comparing feed water and RO permeate.
For commercial and industrial applications, a properly designed reverse osmosis system can significantly reduce dissolved solids. However, pretreatment, post-treatment, disinfection, and routine monitoring must also be considered when producing drinking water.
If you are planning a drinking water treatment project, contact Xinjieyuan through to discuss your application and equipment requirements.
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