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  • Context (DTE): Experts warn that Reverse Osmosis (RO) water with dangerously low levels of mineral content can have an adverse impact on health.
  • Reasons to prefer RO water: Concerns about tap water quality, contaminated groundwater, and irregular water supplies.
  • The water purifier market in India is expected to double from $3,080.7 million in 2023 to $6,880.3 million by 2032.
  • Despite its dominance, the effects of RO water on health and industry regulations remain unclear.

Need for RO water purification systems

  • Water contains helpful microscopic organisms and essential minerals like calcium and magnesium, which aid in muscle and heart function.
    • Sodium, potassium, copper, iron, and zinc are also present in small amounts.
  • Polluted water can carry disease-causing microbes, fertilisers, and heavy metals like chromium and lead.
  • Groundwater may contain elements like fluorides and heavy metals such as chromium, arsenic, and lead, which can cause health issues if consumed in large amounts.
  • The presence of minerals and heavy metals in water is known as total dissolved solids (TDS), responsible for its taste and hardness.
  • High levels of total dissolved solids (TDS) in water can cause unpalatable taste and hardness.
  • Reverse osmosis (RO) systems are becoming popular for purifying water as they can remove impurities and lower TDS levels.
  • An RO system consists of a semi-permeable membrane with tiny pores (0.0001 to 0.001 microns in size) that separate dissolved salts and impurities from water under pressure.
  • As untreated water passes through the membrane under applied external pressure, dissolved salts, impurities, and germs are separated, providing clean and sweet water.

Issues with RO systems

  • RO systems claim to remove 90-100% of TDS. However, essential minerals like calcium and magnesium are also lost in the process.
    • This loss could be a public health concern as many people in the country suffer from micronutrient deficiency.
    • In most houses surveyed by SPECS, RO water has TDS levels of 18 to 25 mg/l, which is considered unsuitable for drinking. ( PECS, an NGO in Dehradun
    • According to SPECS, drip candle filters can be used for purification in many areas. However, due to a lack of awareness, people opt for RO systems unnecessarily.
  • In August 2023, a study by researchers from Medical College Baroda found that RO systems remove 90-92% of beneficial calcium and magnesium.
    • The study, published in the Journal of the Indian Medical Association, linked RO water usage to joint pain among urban citizens of Vadodara.
  • Another study in Vadodara, published in January 2022, found that RO water causes micronutrient deficiency.
    • It analysed patients at SSG Hospital in 2017-18 and found a significant association between RO water usage and vitamin B12 deficiency.
    • Factors like a vegetarian diet, dark complexion, and socio-economic status were also linked to vitamin B12 deficiency.
  • In a 2005 paper, the World Health Organization (WHO) documented cases from the Czech and Slovak populations.
    • They began using RO systems in home taps around 2000-02.Shortly after, complaints of cardiovascular disorders, tiredness, weakness, and muscular cramps emerged.
    • The WHO paper suggests acute magnesium (and possibly calcium) deficiency as the cause.
  • BIS cautioned in its 2015 standards that RO systems aren’t suitable for areas where arsenic levels exceed 0.1 mg/l and fluoride levels surpass 8.0 mg/l, but this was removed from the updated 2023 standards.

Various Methods to Remove impurities from Water

Methods to Remove impurities from Water - PMF IAS

Methods to Remove impurities from Water - PMF IAS

Methods to Remove impurities from Water - PMF IAS

Methods to Remove impurities from Water - PMF IAS

Steps taken

  • National Green Tribunal (NGT) in May 2019, the Union Environment Ministry directed the issuance of a notification to prohibit the use of RO purifiers where TDS in water is less than 500 mg/l. Wherever RO is allowed, a requirement was set for more than 60% water recovery.
    • The report stated that RO systems are not useful if TDS is less than 500 mg/l.
    • It also highlighted the removal of important minerals and wastage of water by RO in such cases.
    • In March 2022, the Supreme Court stayed the NGT order following a challenge by the Water Quality India Association, a non-profit in Mumbai.
  • The Union environment ministry issued the Water Purification System (Regulation of Use) Rules, 2023, In November.
    • These rules provide guidelines for managing reject water and discarded elements from purification systems. RO companies have one year to comply with these rules.
  • WHO’s 2017 drinking water standards recommend TDS levels between 600 and 1,000 mg/l. However, there’s limited data on whether high or low TDS affects health.
  • Bureau of Indian Standards (BIS) has set the maximum TDS limit at 500 mg/l since 1991. Europe, the US, and Canada set TDS standards at 500 to 600 mg/l

Way forward

  • Experts suggest that the necessity of RO depends on the region and water condition, recommending it only for areas with hard surface or groundwater.
  • In places where surface water is used for drinking, a combination of candles, activated carbon, and UV filters is usually sufficient to purify the water.
  • Experts urge that the water supplied through pipes to every household should meet BIS standards, eliminating the need for RO in such areas.
  • Yellowness in water indicates excess iron or bacterial infection, which can be eliminated by boiling (According to the National Institute of Hydrology).
  • Water with low TDS is termed hungry water. Drinking such water gradually absorbs enzymes and minerals from the body, potentially leading to issues like diarrhoea.


  • Flow Direction: Less concentrated solution High concentrated solution.
    • For example, if you had a container full of water with a low salt concentration and another container full of water with a high salt concentration, and a semi-permeable membrane separated them, then the water with the lower salt concentration would begin to migrate towards the container with the higher salt concentration.
  • Osmosis is a naturally occurring phenomenon. Examples of osmosis are when plant roots absorb water from the soil and our kidneys absorb water from our blood.
  • No energy required.

Reverse Osmosis - PMF IAS

Reverse Osmosis

  • Flow Direction reversed: High concentrated solution Less concentrated solution (under pressure)
  • Reverse Osmosis works by using a high-pressure pump to increase the pressure on the salt side of the RO and force the water across the semi-permeable RO membrane, leaving almost all (around 95% to 99%) of dissolved salts.
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