RO Technology for Water Purification

RO Technology for Water Purification

Boon for the Right Places & Bane for the Wrong Places

Any untreated/natural water is known to contain contaminants classified under Physical, Chemical and Biological categories. Physical contaminants include visible contaminants like mud/dirt, sediment or suspended materials. Chemical contaminants include naturally occurring organic chemicals, salts, metals, pesticides etc. but of these, mineral salts are desirable to some extent. Biological contaminants include microbes like bacteria, viruses and parasites (cysts).

Physical contaminants can be removed largely using basic pre-filtration techniques commonly used in many water purifiers. Biological contaminants can be removed using various technologies like UV, ozonation, ultrafiltration, biocidal resins and allied materials. However, a key challenge is removing the dissolved chemicals/solids due to its size and complex nature. While activated carbon can remove some organic chemicals and chlorine, it cannot remove heavy metals and pesticides effectively. This is where RO enters the picture. Reverse Osmosis (RO) is a membrane separation process in which the water is passed under high pressure through a semi-permeable membrane. This process removes excess TDS (Total Dissolved Solids), chemical contaminants like Nitrate, Fluoride, Arsenic, other heavy metals & Pesticides from water to make it safe for drinking. About 20-30% of purified water is achieved and 70-80% water with high contaminant concentration is drained (‘reject’ or ‘waste’ water).

RO cannot be universally applicable for all water types due to key technology limitations.Since RO works on very tiny pore-sized membranes molecularly separating out dissolved chemical contaminants, it cannot, by design, discriminate between so-called ‘good’ and ‘bad’ chemicals. Therefore, it is essential to use RO technology only for waters where the resulting benefits exceed its limitations.

RO is a preferred technology in the areas where safety and other benefits take precedence over water wastage:

  • Water with TDS (Total Dissolved Solids) more than 500 mg/L. As per Bureau of Indian Standards (BIS), acceptable limit for TDS in potable water is 500 mg/L and for Hardness (Calcium+Magnesium), it is 200 mg/L.
  • In today’s world due to deterioration of fresh water sources and colossal increase in population, usage for groundwater high in dissolved solids has unfortunately become more common. Many people complain of ‘heaviness’ or ‘salinity’ in the water when TDS exceeds 500 mg/L or when hardness (Calcium and Magnesium) exceeds 200 mg/L. To make this water potable as per BIS norms, and to achieve acceptable taste, RO usage is vital.
  • Long-term consumption of such high TDS water can result in excess mineral agglomeration causing stress on kidneys, and also leading to kidney ‘stones’, which is an acute health issue.
  • Additionally, due to anthropogenic activities, we find high levels of heavy metals like lead, arsenic and other contaminants in the input water that must be removed by RO in a household application to render safe drinking water. Other technologies (like UV or boiling or resin-based) cannot remove these heavy metals to acceptable global standards.

Areas where RO benefits are marginal compared to water wastage:

  • Water below 500 mg/L TDS, more specifically below 200 mg/L TDS, when subjected to RO treatment leads to potable water with very low mineral content, which could deplete essential minerals for the body in long run. This is because source water below 200 mg/L TDS is already likely to have less than 70 mg/L of Calcium and Magnesium, both essential minerals. However, it must be pointed out that water is not the main source of minerals or nutrients for a human being – food is. More than mineral depletion, the strongest reason why RO should be avoided in low TDS areas is to avoid waste of water as 70-80% of water is drained when RO is used.
  • For waters between 200-500 mg/L, which can be a transition range where taste and/or health factors can influence a purchase decision, both RO and other treatment technologies can be used as individual taste preferences and household conditions also matter. Here, the responsible choice may be to avoid RO because many consumers may still find water acceptable in taste up to 500 mg/L TDS, unless specific medical conditions (such as diagnosis of kidney stones) exists in a household, which will necessitate use of RO even in 200-500 mg/L cases.

Thus, it is essential to use RO technology in appropriate water conditions rather than use it indiscriminately. The end-consumer must be made aware of both the positives and limitations of RO technology and must be educated to use, as per their household requirements, preferences and quality of input water.

Eureka Forbes believes in the ‘right product for the right market’ – that has been our philosophy from inception. One outcome of this philosophy is our strong recommendation on testing the water quality in each home before purchase decision so that we can recommend the right model from over 40 models of water purifiers that we make, each with its own set of benefits and underlying technologies. The following table is offered as illustrative guide to summarize the foregoing analysis. In the table, IS 10500 refers to potable water quality standard set by Bureau of Indian Standards.

TDS All other Chemical parameters within IS 10500 limits? Recommendation on RO technology Comments
Less than 200 mg/L Yes Not recommended. Alternate technologies like UV, UF, resin, available. Don't use RO, unless a doctor prescribes RO for medical reasons
200 – 500 mg/L Yes Not desirable. Alternate technologies like UV, UF, resin, available. Also, a customized RO solution specially designed for these TDS ranges can be considered. Don't use RO, unless a doctor prescribes RO for medical reasons (or) if water is too hard to taste (>200 mg/L of Ca and Mg)
More than 500 mg/L Yes Recommend RO This level is above the tolerance range for most consumers on 'salinity' and associated hardness.
Any No (especially heavy metals like Lead, Arsenic, Chromium and anions like Fluoride and Nitrate are in excess) Recommend RO To remove the health-impacting contaminants considering the safety of water.

Since water quality changes in India due to both human and natural factors, it is imperative to test the source water at the time when purchase of water purifier is being considered. Therefore, the above table is only an illustrative guide.