New Delhi: If I say that pure water does not have any taste, many of you will frown at me. Pure water comprises the elements of hydrogen and oxygen in the proportion of two parts to one. The water we drink contains essential salts and minerals like calcium, potassium, and magnesium, besides hydrogen and oxygen.
These minerals make up the acceptable levels of TDS (Totally Dissolved Solids). Besides, these minerals, the source water contains heavy impurities like arsenic, antimony, lead, iron, etc. It also includes carbonates, fluorides,sulphides, and other salts picked along the way. These contaminants enhance theTDS levels to unacceptable levels.
Who decides the TDS acceptability levels?
BIS (Bureau of Indian Standards) determines the TDS acceptability levels in drinking water. In India, drinking water can contain TDS up to 500ppm or 500 mg/litre. BIS has constituted the following table that could clarify matters further.
TDS Levels mg/litre - Reasons for Acceptability or non-acceptance
Less than 50 Unacceptable – The water with these TDS levels does not contain the minerals required for healthy human growth.
50 - 150 Acceptable – Such TDS levels are usually due to minor industrial contamination.
150 - 250 Acceptable – BIS considers water with this TDS levels as the healthiest of all because it is excellent for cardiovascular health.
250 - 350 Acceptable – Many areas in India depend on groundwater or borewells for their water requirements. This water contains essential minerals. Hence, it is an acceptable range
350 - 500 Fair – The maximum TDS levels acceptable for human consumption is 500.
Above 500 - 1200 Not Acceptable – BIS does not recommend any TDS level above 500 as fit for human consumption. However, water with TDS levels up to 1200 can be subjected to purification using Reverse Osmosis (RO) technology to eliminate TDS and bring it down to acceptable levels
Above 1200 Not Acceptable – Unfit for human consumption
We have discussed the TDS acceptable levels. There is another concept of TDS palatability.
BIS has standardised the minimum requirement of TDS palatability. Both these concepts together determine the overall levels fit for human consumption.
TDS Levels mg/litre and Palatability Quotient
Any level of less than 300 BIS considers any TDS level less than 300 as excellent for drinking. However, water with TDS levels below 50 does not have any taste.
More than 300 and up to 500 These levels as acceptable as the water contains minerals essential for growth.
500 - 900 BIS considers these levels as fair enough because you can use water purifiers to eliminate excess TDS and bring down the levels below 500
Above 900 - 1200 Water with TDS levels in these levels requires multi-stage filtration, including RO, UV, and UF to remove TDS and other contaminants.
Above 1200 BIS considers any TDS level above 1200 as totally unfit for human consumption.
Final thoughts
TDS is not as harmful a word as it is made out to be. TDS levels up to 500 should be acceptable for drinking. Anything above 500 and up to 1200 can be subject to purification to eliminate the excess TDS. Some amount of TDS is necessary to make the water palatable.
—UNI