Is RO Water Harmful? Good For Health? Safe to Drink?

What is pure water? Rig Veda, describes the properties of pure drinking water. It says “Sheetham Sushihi Sivam, Istham, Vimalam lahu Shadgunam.” It defines pure water as that which is “cold to touch, clean has nutritive value, requisite minerals, and trace elements, is transparent, and having its acid-base balance within normal limits.”

Our chemistry books in school teach us that water is a tasteless, colorless, and odorless liquid. So yes, 100% pure water (H2O) does not have any taste.

So, how is it that the water near the river sources has a pleasant taste? It is because the river water collects natural minerals from the rocks in the mountains as it flows down. These minerals include calcium, potassium, magnesium, and many more.

Contamination on the way

As the water flows down the mountains and reaches the plains, it collects various impurities like sand, mud, and harmful organic and inorganic chemicals. Moreover, human settlements along the river banks contaminate the water further.


Besides, industries let out their harmful effluents in the river water. As a result, the water becomes highly contaminated when it reaches the cities on the way towards the sea.

These contaminants include lead, arsenic, antimony, ammonium salts, nitrates, fluorides, chlorides, and many more.

Drinking such contaminated water is harmful to health. Therefore, most cities have water purification plants that remove these impurities and make the water potable.

Groundwater Contamination

Today, you have households depending on groundwater for their drinking water requirements. Unfortunately, this water also contains impurities and TDS in high quantities that make the water salty or brackish. As this water is not fit for human consumption directly, such households use RO purification methods to demineralize the source water and make it healthy to consume.

Related: How to check TDS in water

What is RO purification?

RO or Reverse Osmosis is the popularly followed water filtration method used in houses, industries, and city water treatment plants to remove the harmful minerals present in the source water to make it fit for human consumption.


This method involves the use of a semi-permeable membrane through which water is forced at high pressure. As a result, the heavy minerals with molecular weight above 20 do not pass through the membrane and get eliminated as wastewater. The resultant water is thus free of TDS and demineralized. Thus, one can call it nearly 100% pure.

Related: RO water Purifier Explained

Is this water healthy for consumption?

Now the question is whether this RO purified water is ideal for drinking. Though RO purified water is desalinated and demineralized, it is not the best for consumption because of various reasons. First, this water requires retreatment with specific mineral content to make it healthy for consumption.

Health Risks from Consumption of Demineralized water

Scientific experiments have been conducted on laboratory animals, humans consuming demineralized and RO-purified water, and infants drinking beverages made from RO-purified water.

The possible consequences of consuming such demineralized water or water with a low mineral count are as follows.

Low mineral content water can affect the intestinal mucous membrane, metabolism, mineral homeostasis, or other body functions. Our human body mechanism is such that it adds the necessary electrolytes like sodium, potassium, calcium, etc., to this demineralized water by digging into our body reserves. The inadequate body water distribution can compromise the functions of vital organs, leading to health issues like tiredness, weakness, headaches, muscular cramps, and even an impaired heart rate.

Consuming low-mineral content water results in low or no intake of calcium, magnesium, and other minerals required for our healthy body growth.

However, water is not the primary source of calcium and magnesium for our bodies. Though it is freely present in water, we can replenish the required mineral content in alternate ways.

When used for cooking, demineralized soft water can cause substantial loss of essential minerals from food. Scientific tests have shown that losses could be as high as 60% for calcium and magnesium, 66% for copper, 70% for manganese, and 86% for cobalt. Hence, it can result in an overall deficiency of essential minerals in our body. On the other hand, using hard water for cooking has been beneficial as it reported higher calcium content than food cooked in soft water.

Experiments show that low mineral content water is unstable and highly aggressive to materials it comes in contact with. It can dissolve metals and organic substances from water pipes, storage tanks, and even household storage containers. The presence of calcium and magnesium in water is known for its anti-toxic activity. It can prevent the absorption of harmful chemicals like cadmium or lead from the intestine into the bloodstream.    

Desirable Mineral Content In Demineralized Water

The 1980 WHO Report states that salts are leached out of the body because of consuming water with low TDS levels.

Therefore, WHO recommended that the minimum TDS levels in drinking water should be 100 mg/L. However, the optimum TDS levels should be 200 to 400 mg/L for chloride/sulfate waters and 250 to 500 mg/L for bicarbonate waters.

TDS in water

It is also recommended that the minimum calcium levels in desalinated water should be 30 mg/L. Increasing the calcium levels to 30 mg/L reduces the corrosive activity of desalinated water.

Thus, we can infer that consuming demineralized water is not advisable for our health. It needs to have specific levels of TDS for the water to be certified fit for human consumption. The WHO 2017 Report states that the palatability of water with TDS levels up to 600 mg/L is considered good for consumption.

So, what is the solution for it?

A Counterview – Why is RO purification necessary?

Compared to other water filtration methods, RO water purification can remove more than 90% of minerals from the source water. However, it includes lead, arsenic

Simultaneously, one cannot discount the fact that the RO filtration process also removes essential minerals. However, water is not the prime source of essential minerals for our bodies. There are alternatives in the form of food we consume, dietary supplements, fruits, vegetables, meat, eggs, etc.

However, RO purification ensures to remove 90% of the most toxic chemicals from the water that could cause serious damage in the form of long-term health risks. Nevertheless, the lack of essential minerals like calcium and magnesium in RO purified water entails that your body does not get all the beneficial minerals it requires for healthy growth.

Related: Minimum TDS in Drinking water

Can we have the best of both worlds?

The ideal solution would be to eliminate harmful chemicals like arsenic, lead, cadmium, and others, while retaining essential chemicals like calcium, magnesium, potassium, sodium, etc.

TDS Controller
TDS Controller

The RO purification process involves using a semi-permeable membrane that traps the heavy minerals but allows pure water to pass through. The RO purification system is such that the membrane allows materials having a molecular weight of up to 20 to pass through it. However, water has a molecular weight of 18, whereas sodium and calcium have a molecular weight of 22 and 40, respectively. Therefore, it does not allow the essential minerals to flow through it.

The ideal solution is to have a system where you can replenish the lost minerals post RO purification. Hence, you find RO water purifiers coming with TDS controllers and mineralizers that replenish the lost minerals and increase the pH value of water above 7 to make it fit and tasty for consumption.

TDS Controller in RO Water Purifier

As a result, you have RO purified water with all the essential minerals. However, tests have shown that such remineralization filters are not as effective as they claim to be. These filters raise the pH value of water but do little to add effective minerals to the water. Instead, they enhance the TDS levels of RO purified water to the levels specified by WHO to make it fit for human consumption. In addition, there is no guarantee that the remineralization filters add the requisite amounts of calcium, magnesium, and other minerals.

Related: What is TDS Controller


RO purified water is demineralized water as it removes almost all the minerals in the source water. Simultaneously, it also eliminates harmful contaminants like lead, antimony, arsenic, cadmium, etc. Besides, it also removes harmful bacteria from the source water. Hence, we cannot say that RO water is entirely harmful to health. Yes, it does not contain essential minerals, but it also does not have harmful chemicals that could otherwise prove dangerous for human health.     

The ideal solution is to have a balanced TDS level by enhancing the TDS levels of RO purified water post its RO purification process. The use of remineralization filters can provide solutions to a certain extent alone.

Frequently Asked Questions

Here are some frequently asked questions on RO water purification that can help clarify the matter better.

When is RO purification necessary for human consumption?
The WHO Report of 2017 states that water with TDS levels up to 600 mg/L should be fit for human consumption. Under such circumstances, using RO water purification is unnecessary if the source water has lower TDS levels. Therefore, it is better to check the TDS levels in source water before using an RO water purifier.

At the same time, one should also ascertain the quality of source water. For example, if it has harmful chemicals despite TDS levels being less than 600 mg/L, installing an RO water purifier is better.
What is the use of the TDS controller in RO water purifiers?
There is a difference between the functions of a TDS controller and a Mineralizer. The TDS Controller is a screw-based device that controls the TDS levels in the purified water output. A bypass valve allows adding an adjustable percentage of source water bypassing the RO membrane to the output water to increase its TDS levels. This water is then filtered through a UF/UV or carbon filter to remove contaminants.

Using a TDS controller is a flexible arrangement that can be set at different levels to increase TDS in water without changing the water purifier. In addition, it is an economical and environmentally friendly device.

On the other hand, the primary drawback is that the output water is not 100% RO purified water because it will contain almost all the minerals/contaminants present in the source water but to a lesser degree.
How does a Mineralizer function?
The Mineralizer is different from a TDS controller as it adds alkaline minerals to RO purified water. The mineralizer comprises a cartridge containing carbon, mineral balls, anti-bacterial balls, tourmaline balls, pH booster balls, ceramic balls, etc. The RO purified water passes through this chamber. It helps extract the minerals from these balls to make the water alkaline.

The advantage of using a mineralizer is that it ensures that heavy metals like lead, cadmium, arsenic, etc., do not re-contaminate the water as in using the TDS Controller. However, there is a drawback because you cannot control the TDS levels of output water. A good cartridge should maintain TDS at acceptable levels. However, inexpensive cartridges can prove counterproductive. Besides, the mineral cartridge needs replacement every six to nine months, making it an expensive affair.
Why do RO water purifiers waste a lot of water?
As the RO membrane squeezes out the heavy chemicals from source water, the purified water makes its way through the water storage container. At the same time, the impure water finds its way out of the machine through a separate outlet. Though this water is not fit for human consumption, you can use it to wash dishes, water your plants, and other similar purposes.

Today, you have specific water purification technology that reuses the wastewater and recycles it through storage tanks specifically provided for this purpose. Kent calls it Zero Wastage Technology.

Final Words

Even if we go by the definition of pure water according to the Rig Veda, it should contain essential minerals and have the perfect pH balance to be palatable. Water with an ideal pH level of 7 is 100% pure but does not have any taste or nutrition. Therefore, it is essential to add minerals and make the water alkaline by enhancing its pH value above 7. RO water purifiers come with solutions like TDS Controllers and Mineralizers to ensure the replenishment of essential minerals.

Finally, we can conclude by stating that 100% RO purified water is not advisable for consumption. It is not really harmful to health, but one can always do with some TDS in water to improve its taste and nutritional factor. WHO guidelines also support this by stipulating that TDS levels up to 600 mg/L are permissible for human consumption.


Please enter your comment!
Please enter your name here