What Is The Minimum TDS For Drinking Water?

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RO water purifiers are a boon to people living in places with high TDS water supply. But often, they are projected as villains for depleting useful minerals from drinking water and adversely affecting our health. This raises an important question: What should be the minimum TDS for drinking water? Let us explore in detail what is TDS, its significance and what the TDS ideally should be.

What Is TDS?

minimum tds of drinking water

TDS refers to Total Dissolved Solids. The solids here refer to metals, minerals, ions, inorganic salts etc. They include calcium, magnesium, carbonates, bicarbonates, chlorides, sulfates, fluorides etc.

TDS by itself is not harmful. Rather, the contents that make up the dissolved salts indicate whether the water is harmful or not. In fact, many of these dissolved solids like calcium and magnesium are favourable to human health in limited quantities. But, some are not.

Harmful Dissolved Solids In Water

Representative image of water pollution

A high TDS level is an indicator of harmful contaminants like iron, sulfate, bromide and arsenic, especially when it is a result of water pollution or wastewater discharges.

In India, drinking water is predominantly obtained from groundwater in both rural and urban areas. The water in the majority of the places is highly contaminated with pesticides, metals and even radiological wastes.

According to the groundwater quality report by the government, a number of places along the coastal regions have highly saline water supply. Around 192 districts in 19 states including Andra Pradesh, Gujarat, Haryana, Karnataka, Maharashtra, Orissa, Rajasthan, Tamil Nadu, UP, West Bengal etc have fluoride levels higher than the permissible limit of 1.5 mg/L.

Numerous districts in Bihar, Chattisgarh, West Bengal and UP have a high level of arsenic in underground water. A high concentration of iron is found in more than 1.1 lakh habitations in the country. Nitrate levels are higher than the permissible limit of 45 mg/L in numerous districts of Andra Pradesh, Bihar, Karnataka, Kerala, MP, Maharashtra, Orissa, TN, Punjab etc.

So, as you can understand, the source of water in many of the cities, towns and villages in India are poor. Even though ISI standards say 500 mg/L is an acceptable limit of TDS in drinking water, you cannot be sure that the water you drink is safe unless you analyse the level of harmful contaminants in it.

Role of RO In Providing Safe Drinking Water

As mentioned, arsenic, iron, fluorides, nitrates and sulfates are some of the harmful contaminants found in groundwater in India. Out of these, arsenic, iron and such metals can be removed from water using UF( ultra filtration) membrane. The advantage of UF is that no water is wasted in the filtration process. But the only method feasible at the domestic level to remove dissolved solids is RO ( Reverse Osmosis).

That is why reverse osmosis has an important role in providing safe drinking water in places with poor-quality water.

Unfortunately, sometimes, RO water purifiers are used when it is not a necessity. If the water TDS is less than 250 or if your water doesn’t have a high level of contaminants like fluorides, nitrates or sulfates, you don’t need to use an RO water purifier. And this can have an adverse effect on the environment.

Related reading: How To Choose Water Purifier For Your Home?

Environmental Impact of RO Water Purifiers

RO water purifiers have an adverse effect on the environment because of the water it wastes. For every litre of filtered water, 3 litres are wasted. Such wastage is criminal in a country where 50% of people don’t have access to clean water.

This is the prime reason why the National Green Tribunal ( NGT) has banned the use of RO water purifiers in places where TDS is less than 500. But even then, the expert committee does not recommend banning RO water purifiers if critical impurities like nitrates and fluorides are more than the acceptable limits.

To minimize water wastage, NGT also recommends setting the TDS level of the filtered output water to 150 mg/L. But this unfortunately is not always possible especially when the level of harmful contaminants is high. Also, often, water doesn’t have a palatable taste when TDS is around 150. Reading between the lines, it seems that many government agencies recommend keeping a higher TDS level as it helps save water, and not because low TDS water affects health.

To minimize the negative impact of using RO, it is recommended to utilize the wastewater for other purposes. Some of the ways to use the water are for watering plants, mopping the floor, cleaning utensils etc.

What Should The TDS Ideally Be?

Most RO water purifier manufacturers recommend the minimum TDS level of drinking water should be 50-150 mg/L. But such a blanket statement may not be applicable to everyone. This is because rather than looking at just the TDS level, you should look at the composition of the dissolved solids. Even if the TDS level is 50, but the level of fluoride is higher than 1.5mg/L, the water will not be fit for drinking. Hence, you need to test the water and analyze the content and ensure it is fit for drinking.

Further, we have often noticed that the water may not be palatable when the TDS level is above 50-75 mg/L. Of course, some people adapt after a while. But if you are unable to adapt even after a month or so, you may have to adjust the TDS to a suitable level.

So, while it is ideal that you set the TDS to 150 mg/L, it is not a feasible option for many considering the poor quality of the water supply we receive. The best way is to test the water to be sure of the content and set the TDS of your water purifier accordingly. If not, set it at 150 and observe the taste and if there are any adverse health effects. If so, gradually reduce the TDS to a level that you may find ideal.

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