RO (Reverse Osmosis) water purifiers have become very popular in India. Because RO Water Purifiers are great at getting rid of water hardness, turbidity, and harmful micro-organism, people just rushed to buy these water purifiers even if the TDS in source water at their home was much lower than the recommended level of 500 mg/litre. With the result, many people ended up drinking water that was too low in TDS (dissolved minerals), acidic, and often tasteless.
And its not just about the taste, it actually is harmful to drink de-mineralized water which is acidic in nature and may result in digestion problems, weaker bones and other mineral deficiencies.
To fix this problem, RO manufactures came up with two solutions. Some started using a TDS controller and other started using an alkaline mineral cartridge to add minerals back to the RO purified water.
In this article we will discuss the pros and cons of these two methods and also know about the ideal TDS in RO water.
Table of Contents
- Reverse Osmosis – What is It?
- What is TDS?
- Recommended Levels of TDS in RO Water
- Why We Need a TDS Controller or Mineral Cartridge
- TDS Controller/Adjuster
- Alkaline Mineral Cartridge
- TDS Controller Vs Alkaline Mineral Cartridge
- Top 3 RO Water Purifiers with a TDS Controller
- Top 3 RO Water Purifiers with an Alkaline Mineral Cartridge
Reverse Osmosis – What is It?
Reverse osmosis (RO) is a water purification technology that uses pressure to pass source water through a semi-permeable membrane with pores small enough to pass pure water through but rejecting dissolved salts (ions) and impurities like bacteria and virus.
While there are other methods of purifying water (like UV rays) that get rid of all microorganisms like bacteria and virus, but there is no other method available to get rid of dissolved salts (TDS) in the water.So, it is the requirement to reduce TDS or heavy metals in water, which makes the use of RO filtration necessary for water purification.
What is TDS?
TDS or total dissolved solids is the amount of dissolved organic and inorganic impurities in water. This includes calcium, magnesium, potassium, sodium, carbonates, nitrates, bicarbonates, chlorides, sulfates, and a small amount of organic matter such as leaves, silt, and plankton. In some areas (usually heavily polluted), the TDS in water includes toxic ions of heavy metals such as lead, nitrate, cadmium, and arsenic.
The composition of TDS in water will depend on the composition of rocks/soil in the area, presence of industries, sewage/waste water discharge, quality of river water (if present), air pollution from industries and automobiles (resulting in acidic rain), agricultural runoff (chemicals from fertilisers and pesticides), urban runoff, and various other factors.
Is High TDS Always Harmful?
High TDS by itself isn’t necessarily unhealthy. However, high TDS levels are frequently accompanied by concentrations of other substances (usually the heavy metals like arsenic, chromium, cadmium, mercury, lead, and a few others) that are harmful to health.
At the same time if you live in an area where there is no industrial waste discharged into soil or water bodies, and no one uses synthetic pesticides or fertilisers in their agricultural farms, then the water available in such an area would normally be very healthy. Even if the TDS count of underground water in such an area reaches up to 1200 mg/litre, it would still be safe for humans.
All it will have is useful minerals and bicarbonates in the water which are not harmful and our bodies are naturally able to handle such natural mineral water. There can be some exceptions of-course.
High TDS is a problem when there are toxic chemicals present in the source water. Or when the TDS is greater than 1200 mg/litre. Such water is then unpalatable.
Recommended Levels of TDS in RO Water
Ideal TDS in Drinking Water
Taste of Water with Different TDS Concentrations
High levels of TDS in drinking-water may have a certain objectionable taste because of salts. At the WHO, a panels of water tasters rated the taste of water in relation to the TDS level. This is what they observed:
|Level of TDS (mg/litre)||Rating|
|Less than 300||Excellent Taste|
|300 – 600||Good Taste|
|600 – 900||Fair Taste|
|900 – 1,200||Poor Taste|
|Above 1,200||Unacceptable Taste|
Recommended TDS in RO Water
RO water purifiers that come with a TDS controller gives you the ability of controlling the TDS of output water. While there is no guideline about it from the government, we can take a clue from the studies done by the WHO.
WHO suggests that TDS in drinking water should never go below 30 ppm or else its a risk to your health. Another WHO study as quoted above, found that water tastes best when the TDS is under 300 mg/litre.
From all this, we can conclude that the ideal TDS of drinking water should be anywhere between 50 to 300 mg/litre. If you don’t want a range but a single number, then take the average and it would be around 180 mg/litre.
However, if the source water at your home is contaminated with heavy metals, then it may be better to keep TDS level at 90 mg/litre. This is because TDS controller will add minerals from the source water and it will include every mineral present in the source water in small quantity.If you ask us, we would suggest to keep the TDS levels of water between 90 – 200 mg/litre (ppm) depending on the pollution level in your area.
If you want to be sure, then you should get the source water tested by a government water supply agency or laboratory. Alternatively, you can test the water at home using the products listed below. The test you do at home are not accurate but they give you an idea.
Why We Need a TDS Controller or Mineral Cartridge
RO water purifiers reduces the TDS of water by 90-95%. When this kind of purifier is used with water that has TDS between 100 to 500 mg/litre, then the output water is extremely low in TDS. It can have a TDS of 10 mg to 50 mg/litre. Such water may be harmful for health and may even be acidic in nature. Your body will have to work extra to fix its mineral contents and its PH.
The National Green Tribunal of India, has recommended Govt of India to ban RO water purifiers in areas where TDS in source water is less than 500 mg/litre for this very reason and for the reason that RO wastes too much of water in the process of purification. This shows that the problem is real and if we use a RO water purifier, we must constantly check the TDS in output water and adjust TDS using TDS controller or by changing the mineral cartridge.
TDS controller is a screw-based device that controls the level of salts in the purified output water. It works as a bypass valve which takes a percentage (adjustable) of source water bypassing RO membrane to the output water, which is then filtered through a UF or carbon filter, and/or UV chamber. Number of filtration methods and the sequence used varies from model to model.
How does a TDS controller work?
The water going into the reverse osmosis filter is divided into 2 parts. One part goes into the RO membrane and undergoes RO purification. The second part of water does not go through the RO membrane. It goes through a UF membrane or a UV Chamber, depending on the RO specifications.
The output water would be a mixture of water purified in Part 1 plus a small portion of Part 2 water. The mixture is controlled through a valve connected to the Part 2 assembly, thus controlling the TDS.
Advantages of TDS Controller
Flexibility: Having a RO water purifier gives you the flexibility of adjusting the TDS levels in output water as per your choice. You can set it to 150 mg/litre today and later if you change your mind, you can set it to any other limit without changing the water purifier. Also, if you want, you can close the water coming from part 2 completely and the output water would be 100% RO purified water.
Economical: TDS controller is a cheap device and costs around 100 rupees only. Further, it is a one time expense and you won’t need to change it for several years.
Natural: Because TDS controller adds minerals from the source input water, it has a wide variety of minerals naturally present in the water. Therefore this kind of water is more natural.
Disadvantages of TDS controller
Not 100% Pure: The output water from a RO water purifier with TDS controller may not be very pure. Because the TDS controller mixes a part of water that did not go through RO membrane to the output water, it will have all the minerals and chemicals present in it that were originally present in the input water, though in much smaller amount.
This is usually not a problem unless the source water is heavily polluted with heavy metals like lead, nitrate, cadmium, and arsenic. As long as the output water has these heavy metals under the safe limit, it would be safe to consume such a water.
Alkaline Mineral Cartridge
Some RO water purifiers use an alkaline mineral cartridge to add minerals back in the purified water. A mineral cartridge typically contains several layers of different materials. These may include pelletized activated carbon, mineral balls, PH booster balls, antibacterial balls, ceramic balls, tourmaline balls, etc.
How does an Alkaline Mineral Cartridge work?
After the water has passed through the RO membrane, it is then made to pass through a mineral cartridge. During the process, it extracts minerals from the mineral balls present in the cartridge. Some cartridges come with PH booster balls and in that case, the PH of water improves and the water becomes alkaline.
The quality of mineral cartridge used is very important here as it would decide the variety of minerals that get added to the purified water. Some mineral cartridges also claim of providing additional benefits by energising water, and more.
Advantages of Alkaline Mineral Cartridge
Best Protection Against Heavy Metals: RO water purifiers with a mineral cartridge and no TDS controller offer the best protection against pollutants, pesticides, and heavy metals. It is because it provides 100% RO purified water and the additional minerals added come from the mineral cartridge that only contains healthy minerals like calcium and magnesium.
Disadvantages of Alkaline Mineral Cartridge
No control over TDS of output water: If your RO water purifier uses a mineral cartridge, then the output water TDS would depend on the TDS of source water and the quality of mineral cartridge.
The RO filtration would decrease TDS of purified water by 90 to 95%. A mineral cartridge would add 20mg/litre to 80mg/litre TDS to the purified water.
For example, if TDS of input water is 200mg/litre, the output water would have a TDS of 10 to 20mg/litre after passing through RO membrane. After passing through a mineralizer, it would have a TDS of 40 to 100 depending on the quality of mineral cartridge used.
If the mineral cartridge used is not very good, then the TDS of output water in this case would be just 30 or 40mg/litre which is unacceptable.
In any case, you will not be able to adjust the TDS as per your choice.
Recurring Cost: Mineral cartridge, would need to be replaced every 6 to 9 months depending on the usage. This adds to the annual cost of maintaining a RO water purifier.
TDS Controller Vs Alkaline Mineral Cartridge
|TDS Controller||Mineral Cartridge|
|Suitable for source water with TDS under 900 mg/litre and no or very low amount of heavy metals present in it.||Suitable for source water with TDS 900 to 2000mg/litre. Or where the source water is contaminated with heavy metals due to pollution.|
|Full control over TDS of output water||No control over TDS of output water.|
|Economical||Adds rupees 1000 to 2500 to the annual maintenance cost.|
Top 3 RO Water Purifiers with a TDS Controller
Top 3 RO Water Purifiers with an Alkaline Mineral Cartridge
Looking for water purifiers in a certain budget? Check the following posts:
TDS controller and mineral cartridge both are good at increasing the TDS count in RO purified water. Which one you choose depends on your personal choice and also on the TDS count and presence of heavy metals in the source water.
We recommend RO with TDS Controller if the source water has TDS less than 900mg/litre with negligible amount of heavy metals. For water with TDS 900 to 2000mg/litre, we recommend a RO purifier with mineral cartridge.
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