According to a recent report by NITI Aayog, it is estimated that more than 600 million Indians are facing high to extreme water stress. At least 163 million people do not have access to treated piped water and a whopping 70 percent of the water supply is contaminated, resulting in lakhs of deaths each year. India ranks at a miserable 120th out of 122 nations in the water quality index.
To combat these glaring inefficiencies, the Government of India has launched JalJeevan Mission that promises a supply of clean drinking water to every household including rural households by 2024. The Bureau of Indian Standards has recently published a revised set of standards for drinking water keeping the JalJeevan Mission in point of view.
So what is TDS and why is it important?
TDS is nothing but the Total Dissolved Solids present in a sample of water. Water being a universal solvent, it dissolves everything it comes in contact with before forming reservoirs of groundwater or surface water.
The dissolved minerals in water are commonly referred to as Total Dissolved Solids (TDS). The minerals are basically compounds (salts) of Calcium(Ca), Magnesium(Mg) such as Calcium or Magnesium Chloride, Calcium or Magnesium Sulphate ( CaSo4, MgCl, etc). The TDS content of any water is expressed in milligrams /litre (mg/l) or in parts per million (ppm). The TDS in water may also include heavy metal residues of Lead, Cadmium, Mercury and Arsenic, which are harmful even in small quantities. Other than minerals, TDS is also a measure of small amounts of organic matter present in the water sample.
According to WHO, the presence of dissolved solids in water may affect its taste. The palatability of drinking water has been rated by panels of tasters in relation to its TDS level as follows:
- excellent, less than 300 mg/litre
- good, between 300 and 600 mg/litre
- acceptable, between 600 and 900 mg/litre
- poor, between 900 and 1200 mg/litre
- unacceptable, greater than 1200 mg/litre.
Water containing TDS concentrations below 1000 mg/litre is usually acceptable to consumers, although acceptability may vary according to circumstances. However, the presence of high levels of TDS in water may be objectionable to consumers owing to the resulting taste and to excessive scaling in water pipes, heaters, boilers, and household appliances. Water with extremely low concentrations of TDS may also be unacceptable to consumers because of its flat, insipid taste; it is also often corrosive to water-supply systems.
According to BIS, the following standards apply to organic matter including bacteria, viruses, and other pathogens:
- Water should be free from coliform bacteria in the water sample
- Enterovirus, reovirus, and adenovirus have been found in water, the first-named being the most resistant to chlorination. If enterovirus is absent from chlorinated water, it can be assumed that the water is safe to drink.
- The biological qualities of water are of greater importance when the supply has not undergone the conventional flocculation and filtration processes, since increased growth of methane-utilizing bacteria on biological slimes in pipes may then be expected, and the development of bryozoan growths such as Plumatella may cause operational difficulties.
- Some of the animalcules found in water mains may be free-living in the water, but others such as Dreissena and Asellus are more or less firmly attached to the inside of the mains. Although these animalcules are not themselves pathogenic, they may harbor pathogenic organisms or viruses in their intestines, thus protecting these pathogens from destruction by chlorine.
- Chlorination, at the dosages normally employed in waterworks, is ineffective against certain parasites, including amoebic cysts; they can be excluded only by effective filtration or by higher chlorine doses than can be tolerated without subsequent dechlorination.
- The cyclops vector of the embryos of Dracunculusmedinensis which causes dracontiasis or Guinea-worm disease can be found in open wells in a number of tropical areas. They are identifiable by microscopic examination.
- Cryptosporidium and Giardia should be absent in 10 liters of water when tested in accordance with USEPA methods.
- The drinking water should be free from microscopic organisms such as algae, zooplanktons, flagellates, parasites, and toxin-producing organisms.
How is TDS measured?
The two principal methods of measuring total dissolved solids are gravimetric analysis and conductivity. Gravimetric methods are the most accurate and involve evaporating the liquid solvent and measuring the mass of residues left. This method is generally the best, although it is time-consuming. If inorganic salts comprise the great majority of TDS, gravimetric methods are appropriate.
Electrical, or specific, the conductivity of water is directly related to the concentration of dissolved ionized solids in the water. Ions from the dissolved solids in water create the ability for that water to conduct an electric current, which can be measured using a conventional conductivity meter or TDS meter.
All said and done TDS measurement only offers a preliminary measurement of TDS in water. For instance, the water could contain low concentrations of heavy metals like Arsenic, Mercury, and Lead which when accumulated in the human body over a period of time can cause neurological damage. They particularly affect children whose immune systems are not as developed as those of adults.
What’s the writing on the wall?
Get yourself a TDS meter and keep checking the TDS quotient in your water supply from time to time. According to BIS, 500 ppm is the cut-off for unacceptable levels of TDS, beyond which you should opt for a good quality water Reverse Osmosis purifier. The best option is to go for an RO + UV + UF water purifier that eliminates up to 95% of TDS through RO, deactivates microbes through UV lamp usage, and prefiltered using UV technology. Do check the entire range of RO water purifiers from Pureit before you zero-in on an RO water purifier.
Though RO eliminates up to 95% of TDS, it often leaves the water tasteless, insipid, and completely demineralized. Demineralized water is not good for health and this is rectified using a TDS modulator in the water purifier.
How does the TDS modulator work?
The water from your water supply is divided into two halves, where only one half undergoes RO treatment. The other, UV/UF treated half merges with the RO purified water before the water is dispensed through the storage tank, raising the TDS levels up to an acceptable range of 300 – 500 ppm. You can check the TDS quotient of the water dispensed and adjust your TDS modulation accordingly.
If TDS needs to be reduced then the flow of input water from the RO membrane is increased and the flow of input water from Activated Carbon Filter or UF membrane is reduced. If TDS needs to be increased then the flow of input water from the RO membrane is reduced and the flow of input water from Activated Carbon Filter or UF membrane is increased. In cases where the TDS controller is located inside the water purifier, it is best if you seek the assistance of a technician. We recommend that you read TDS guide for a more comprehensive understanding of TDS in water.