TDS level is the vital parameter to measure how healthy drinking water is. But the term normally does not make any sense to people. TDS means Total Dissolved Solvents in the water. This article is your go-to guide about the TDS in water and water purifiers. We will explain what TDS is and also give insights on how you can check the quality of a water based on TDS. There are various ways you can measure the TDS. This shall also be explained later in this article.
What is TDS in Water
TDS indicates the Total Dissolved Substance level in a sample of water. Substances in water that can pass through a 2-micron filter come under TDS. Inorganic and some organic solids contribute to the TDS in water. Water often gets regarded as a universal solvent. It can dissolve a vast variety of substances as the name suggests. Many solids end up in water through natural paths as well as through human activities. TDS analysis reveals the different dissolved solids in the water and their concentrations. This gives an idea about the quality of your water. The presence of TDS in water doesn’t always represent a bad water quality. An ideal TDS level in your water helps to maintain the required essential mineral levels.
You can estimate the amount of TDS in water using a TDS meter or by gravimetric analysis. Higher TDS in water can sometimes cause adverse effects. Water hardness, taste differences and a change in colour, etc could be the result of a higher TDS. Sometimes it may lead to some health issues like gastrointestinal troubles. The effects resulting from higher TDS depend on the metallic salts present in the water. Common cations found in water include calcium, magnesium, sodium, and potassium. Carbonate, bicarbonate, chloride, sulfate, nitrate, etc constitute the common anions. Water purifiers with RO (Reverse Osmosis) filters can reduce the TDS in water. Most of them come with a mineraliser. This ensures the availability of the essential elements we need from the water. TDS in water can become quite disturbing when it exceeds the safe limits. Understanding TDS and ensuring the required level can save you from those troubles.
Water Quality and TDS
Experts don’t consider TDS as a primary pollutant in water. But it becomes a useful tool to analyze many other characteristics of water, like its taste. It offers a tool to examine the wide variety of chemical contaminants present in water. You should note that TDS analysis cannot differentiate between essential with toxic substances. The main components of TDS in water come from water-soluble ionic compounds. An ionic compound contains positively charged ions (cations) and negatively charged ions (anions). Calcium carbonate, which contains calcium cation (Ca2+) and carbonate anion (CO32-) makes a good example. They bind each other with an electrostatic force of attraction. When in water they dissociate into oppositely charged ions, contributing to TDS. Some soluble hydrocarbons also contribute to TDS in water.
TDS comes from natural as well as manmade sources:
- Natural Sources: Runoff water, rainwater percolation, seawater intrusion, etc constitutes some of these sources. Hydrocarbons from decaying materials like humic and fluvic acids also contribute to TDS. Water passing through lime rich/clay rich areas contains excess calcium, magnesium and carbonate ions.
- Manmade Sources: Leaching from pipes and plumping, urban runoff, sewage etc add TDS to the water. These along with industrial and agricultural runoffs constitute examples of manmade sources of TDS. Zinc, arsenic, copper, iron, lead, etc reach water mainly through manmade sources.
TDS affects water quality in different ways:
1. Water Hardness
A high TDS value may imply water hardness. Borewells, water sources near mineral deposits, etc may contain hard water. Hard water makes life hard in many ways. It results from the presence of calcium and magnesium salts (eg, calcium bicarbonate and magnesium sulfate). Many other compounds can also cause water hardness. Soap doesn’t foam well in hard water. Hard water makes your skin and hair dry. Scale formed by salts can cause many problems.
2. Maintenance Troubles
A high TDS value means excess salts in the water. Excess salts in water can cause mineral deposits and scale formation. It also gives rise to corrosion of metal parts made of iron, zinc, etc. These will cause damages to your plumbing system and appliances and contaminate your water. It also affects the aesthetic vibe of your home.
3. Health Concerns
TDS value in itself doesn’t convey any health hazards. It depends on the nature of dissolved solids present in the water. Heavy metal contamination in water can cause serious health issues. Toxic hydrocarbon residues from various sources can also become serious. Chemical contamination from industrial runoffs, pesticide residues from agriculture, etc., can contaminate your water. These along with heavy metals like arsenic, copper, lead, etc causes bio-magnification. Cancers, neurological problems, organ failures, etc can result from these contaminants. TDS doesn’t tell us about individual contaminants and toxicity. We need other methods to distinguish between the contaminants and their levels.
High or low TDS value alters the natural taste of water. A high TDS value may make water tastes metallic, salty or bitter. A low TDS renders water bland and tasteless. Soluble organic components can also alter the taste and smell of the water.
What is the TDS Level of Drinking Water
What should be the ideal TDS required for drinking water? TDS is a vital parameter to check how healthy the water is for drinking. Bureau of Indian Standards (BIS) fixes the standard of drinking water in India. It also considered the studies conducted by World Health Organization (WHO). BIS adjusted those studies to suit the Indian scenario. We have discussed how WHO and BIS standardised the TDS levels for drinking water below.
1. World Health Organisation
A study conducted by WHO gave some limits for the preferable levels of TDS in water.
|TDS in mg/L
|Suitability for drinking
|900 to 1200
|600 to 900
|300 to 600
The study also holds water with low TDS as unacceptable. They suggested this due to the flat, weak taste of water with low TDS. Another study from WHO points out the problems related to the demineralization of water. Demineralization removes even the beneficial minerals from water. It leaves water tasteless and aggressive for leaching. You can read more about demineralization here.
2. Bureau of Indian Standards
BIS has prescribed the limits of TDS for fixed for normal fresh drinking water. It fixed the upper limit of TDS at 500 ppm, but didn’t fix the lower limit. The upper limit can go up to 2000 ppm in the absence of alternative water resources. These limits don’t hold for special cases of contaminations. These include contamination by fluoride, arsenic, etc. In such instances, make use of the special standards created for them. Low levels of TDS reduce the pH of the water. The pH levels fixed for fresh drinking water by BIS come within 6.5-8.5. From this, we can assume the lower limit for TDS as 80 ppm.
Testing the TDS becomes essential to ensure the desirable amount of minerals in your diet. Keeping your water TDS between 500mg/L – 200mg/L gives you the ideal condition.
How to Check TDS in Your Water
There are two methods to check the TDS in water- 1. Using TDS meter and 2. Using Gravimetric analysis.
1. Checking TDS level using TDS Meter
The easiest way to check TDS is by using a TDS meter. TDS meter works based on the conductivity of the sample of water. The conductivity of water results from the charged ions present in it. The concentration of ions becomes directly proportional to the conductivity. You can compare the TDS conductivity results available in laboratory measurements. This gives the approximate concentration of ions, usually within 10% accuracy. A home water test kit or a laboratory analysis can help you identify the individual contaminants. You can buy TDS meters affordably from online sources.
TDS meter offers an easy to use, reliable method for us to estimate TDS. The steps given below can help you in testing TDS using a TDS meter.
Step 1: Remove the top and turn on the TDS meter and turn it on. It should read zero.
Step 2: Dip the tip of the TDS meter into the water that needs to be tested. Make sure that at least an inch gets immersed in water.
Step 3: You can find the result displayed on the display. After noting it, turn off the TDS meter.
2. Checking TDS using Gravimetric Analysis
The gravimetric analysis makes use of mass difference. It compares the masses of the wet sample against the dry sample after removing water content. Gravimetric analysis results hold well when TDS comprises mainly inorganic salts. It might not hold well for samples with volatile components. This method gives better results but consumes a lot of time.
Step 1: A fixed volume of water gets filtered using pre-measured glass filters.
Step 2: The filter gets dried in an oven and cooled down in a desiccator.
Step 3: The filter gets weighed repeatedly. A repeated constant measure indicates the final value.
RO Water TDS Levels
Reverse osmosis usually removes over 95% of TDS. Some RO membranes can reduce TDS below 25. Though sounds impressive, it may not mean good drinking water quality. A low TDS renders water unpalatable and low in essential elements. To maintain desired levels, you need to know what a TDS value means.
|Need for RO
Lack required levels of essential minerals
|Less desirable for drinking
|Suitable for drinking
|Less desirable for drinking
Suitable to drink in the absence of alternatives
Suitable for domestic consumption
|Unsuitable for drinking and domestic consumption
Is 25 TDS Safe for Drinking Water
Natural water never comes with TDS as low as 25. RO membrane usually reduces water TDS below 25. This is why most people often doubt whether TDS of 25 is safe for drinking water. You need to understand that the distillation process in RO purifiers can reduce the 25 TDS even below 10.
A TDS of 25 or below doesn’t mean that the water is unsafe immediately. You can consume it without any worries. But long term consumption of such water can deplete the essential elements in your body. Normal water contains minerals of calcium, chlorine, magnesium, Pottasium, etc. Elements like these play important roles in the constitution and functioning of our body. Continuous consumption of purified water below 25 TDS may result in deficiencies. Keep the TDS in your water around 200-500 to avoid such health issues.
How to Maintain Desirable TDS in Your Water
Maintaining the TDS at the desired level of 200-500 ppm is essential for your health. You can reduce the TDS in water using simple methods. But reducing the TDS doesn’t ensure ideal water quality. You have to ensure the right amount of minerals in water to achieve this. Methods used for these include:
1. Reverse Osmosis
In reverse osmosis water pushes against a membrane with high pressure. This membrane contains microscopic pores. They allow molecules with a size of less than 0.0003 microns to pass through it. As the dissolved solids have higher masses, they get filtered out. This helps to reduce the TDS in water to a great extend.
In distillation, water with high TDS gets boiled to produce vapour. The vapour rising up gets condensed to water by a cool surface. As the boiling point for dissolved solids are higher than water, they get left behind. It can reduce TDS below 5 ppm. You can use a filter with an OS membrane to improve the quality of water.
De-ionization makes use of positive and negative electrodes along with an ion-selective membrane. This method manipulates the charge present on the inorganic ions dissolved in water. These ions accumulate on the oppositely charged electrodes and get removed. De-ionization only removes charged particles. Passing the water through an OS membrane before de-ionizing can solve this problem. This method gives the water of the highest purity.
4. Mineraliser Technology (MIN-TECH)
MIN-TECH offers a hand to restore the essential elements in the water. The above-said methods reduce the TDS in water. They can’t differentiate between essential and non-essential minerals. Mineralisers maintain an ideal range of taste and pH by adding back the required minerals. They form a part of RO membranes filters for drinking water.
TDS doesn’t make the water hazardous or non-consumable. It means the total dissolved inorganic and organic solids present in the water. Dissolved solids reach water through natural and manmade sources. Higher TDS value causes problems like the hardness of water, corrosion and mineral deposition. It may also affect the taste of water and may cause gastrointestinal troubles. BIS gives TDS below 500 ppm as the acceptable level of freshwater. But the water that has a low TDS value lacks in taste and essential elements. A balanced approach can help you maintain the desired water quality. TDS meters and gravimetric analysis offer easy ways to measure TDS. A TDS analysis can’t differentiate between the individual contaminants. The effects of dissolved solids depend on their individual nature. Methods like reverse osmosis, distillation and de-ionisation reduced the amount of TDS. Mineraliser technology helps to keep essential minerals in purified water.