WHAT IS TDS LEVEL?
TDS stands for "Total Dissolved Solids." It is the measure of all inorganic and organic substances that are dissolved in water. Magnesium, calcium, potassium, sodium, chloride and sulphate are some of the most common inorganic substances found in water. To some extent, the presence of these minerals in water is beneficial, but when the level becomes excessive, it is cause for concern. Note: 1 mg/L is the same as 1 ppm, so both units are used in this article.
HOW TDS IS MEASURED?
TDS does not tell you which substances are present, so two samples with the same reading can differ in taste, hardness, and safety. Most handheld meters measure electrical conductivity and convert it to a TDS value. The reading is therefore an estimate, and it changes with water temperature.
IDEAL TDS LEVEL IN WATER
According to World Health Organization (WHO) report on TDS in drinking water, there is a lack of reliable data on potential health effects associated with TDS in drinking water. For the ideal TDS of drinking water, no health-based guideline value is proposed. Because TDS in water can be high due to a variety of factors, the individual constituents of the water supply should be identified in areas where the TDS content of the water supply is extremely high.
The Bureau of Indian Standards (BIS) has established 500 mg/L as the acceptable limit of TDS in drinking water. However, the standard states that if no other source of drinking water is available, this acceptable limit can be relaxed up to 2,000 mg/L. The BIS report also states that if the TDS in the drinking water exceeds 500 mg/L, it may reduce palatability (acceptable taste) and cause gastrointestinal irritation.
Water's taste may be affected by the presence of dissolved solids. Panels of tasters, as reported by the WHO, rated the palatability (acceptable taste) of drinking water in relation to its TDS level as follows:
. <300: Excellent
. 300-600: Good
. 600-900: Fair
. 900-1200: Poor
. >1200: Not acceptable
This acceptable TDS limit only applies to normal freshwater; if the water contains toxic impurities such as arsenic or fluoride, other BIS standards will apply. Each of these contaminants needs its own test, because a TDS reading will not detect them.
WHY THE RIGHT TDS DEPENDS ON THE USE?
There is no single TDS value that suits every purpose. Drinking water is usually comfortable in the range given below. Tea and coffee often taste cleaner at lower TDS, while cooking and rice are less sensitive. Kettles, geysers, steam irons, and humidifiers last longer on water with lower hardness. For infant feeding, follow the advice of your doctor and the product label. Boilers and laboratory work have their own specifications, which are usually far stricter than drinking water limits.
It is important to note that some of the dissolved minerals in water are beneficial to human health, so very low or zero TDS is also not advised. Reducing the TDS level to a very low value also has an effect on the pH level of the water, which BIS specifies should be between 6.5 and 8.5. Water with a very low TDS level will taste bland. IS 10500 sets no lower limit for TDS. Many RO plants add a mineraliser or blend a small portion of feed water to raise very low TDS (roughly below 50 mg/L) back to a pleasant level.
REASONS FOR NON-ACCEPTANCE OR ACCEPTABILITY
. Fewer than 50: This is not recommended. Water with such a low TDS level tastes flat and has very few minerals.
. 50-150: Acceptable: TDS levels in the 50-150 range, on the other hand, are good for daily drinking. If you're using a RO water purifier, make sure the TDS level in the purified water isn't too low (below about 50 mg/L).
. 150-250: Acceptable: This is a well-balanced range for everyday drinking.
. 250-350: Acceptable: TDS varies a lot from one source to another, so check your own water.
. 350-500: Acceptable: A TDS level of less than 500 mg/L is acceptable, according to BIS guidelines.
. 500-900: Not acceptable: Utilize a RO water purifier equipped with a TDS controller or mineralizer.
. 900-1200: Not acceptable: Utilize a RO water purifier equipped with a TDS controller or mineralizer.
. 1200-2000: Not acceptable (BIS allows up to 2,000 mg/L only when no other source is available): Treat the water before drinking. Choose a RO water plant that can remove up to 2000 mg/L of impurities.
. Don't drink if you're over 2000: Most home water purifiers are incapable of purifying water with a TDS level greater than 2000 mg/L. You may need a larger RO plant for such capacity removal.
LOW TDS WATER AND PIPES
Very low TDS water is less buffered and can be mildly aggressive to metal pipework, including copper and galvanised steel. In buildings with metal pipes, a mineraliser or a controlled blend of treated and untreated water may be worth considering. The right choice depends on the pipe material, the pH, and what users prefer.
TDS IN RO PLANTS AND PACKAGED WATER
An RO membrane removes most dissolved solids, so treated water can fall well below the range people prefer to drink. Many plants add a mineraliser or blend a small portion of feed water to bring TDS back to a taste-friendly level. Packaged drinking water must meet FSSAI standards (BIS certification is no longer mandatory), so check the latest rule for your product before you finalise the design.
EFFECT OF A CHANGING SOURCE
Borewell and municipal supply can change with the season, rainfall, and pumping. A TDS reading taken once may not reflect the water you receive in summer or after the monsoon. Test the source more than once a year and adjust the treatment if the reading moves.
TDS AND WATER HARDNESS
TDS and hardness are related but not the same. Hardness comes mainly from calcium and magnesium, and it is the main cause of scale on kettles, geysers, and heating elements. Water can meet the TDS limit and still form scale, so test hardness separately if your appliances are affected.
HOW TO MONITOR TDS?
Test the feed water and the treated water on the same day and record the readings over time. A rising treated-water reading often points to an ageing membrane. For a complete picture, send a sample to an accredited laboratory and ask for TDS, pH, hardness, chloride, sulphate, and iron.
COMMON TDS MISTAKES
Treating a single meter reading as the whole story is the most common mistake. Others include comparing readings taken at different temperatures, assuming low TDS always means safe water, and ignoring hardness, arsenic, fluoride, and bacteria because the TDS looks fine. Use TDS as a first check, and use laboratory analysis for decisions that matter.
FREQUENTLY ASKED QUESTIONS (FAQs)
Q1. Is 500 mg/L TDS safe to drink?
It is the BIS acceptable limit. Water within the acceptable limit meets the Indian standard, although taste varies from person to person.
Q2. Why does my meter differ from the laboratory result?
A meter estimates TDS from conductivity using a conversion factor, so it is approximate. A laboratory measures the solids directly.
Q3. Is very low TDS water harmful?
It is not harmful in itself, but it can taste flat and may be mildly corrosive to some metal pipes.
Q4. Does TDS show whether water is contaminated?
No. TDS gives no specific information on bacteria, heavy metals, or organic compounds. Each needs its own test.
Q5. How often should I check TDS?
For a home RO system, check treated water monthly and check the feed whenever the source changes. For a commercial plant, follow the testing schedule in its specification.
Q6. Is 30 TDS water safe to drink?
A TDS of 30 is far below the BIS limit, but it is very low, so the water tastes flat and has very few minerals. If it comes from an RO purifier, add a mineraliser or blend a little feed water. TDS does not show whether water is free of bacteria or chemicals, so test those separately.
Q7. What are the side effects of high TDS water?
Water above 500 mg/L may taste salty or bitter and, as BIS notes, can cause gastrointestinal irritation. High TDS also leaves scale on kettles and geysers. The health effect depends on what is dissolved, so get a laboratory test if your TDS is high.
Need a water test or an RO plant for high-TDS water? Call or WhatsApp +91-9650608473, or write to enquiry@netsolwater.com.
