RO water purifiers explained: What every homeowner should know

RO units consume power and waste 80% of the water they filter. Many Bengaluru households, in fact, don't need these purifiers at all.

Despite water scarcity, Bengalureans let hundreds of litres of reject RO water down their drains every day without much thought.

For every one litre of filtered water, RO (Reverse Osmosis) water purifiers waste 3.5 litres of water. But many Bengaluru households don’t even require RO purifiers.

“RO water purifiers have become a status symbol. Many residents do not know the purpose of the purifiers, let alone the water quality,” says Vinosh M Paul, independent water purifier sales and service technician in Bengaluru. So, do you need an RO unit? 

What are RO water purifiers? 

Reverse Osmosis (RO) is an advanced technology which can purify even the most contaminated water. RO units were first used in California in the 1950s, mostly for desalination, that is, filtering brackish or saltwater sources to get potable water. It entered the Indian market in 1998. 

osmosis and reverse osmosis
Reverse osmosis works on applied pressure, requiring electricity. Source: Pure Aqua

“RO is the only technology today which can reduce the level of Total Dissolved Solids (TDS) in the water and make it soft,” says Hari Prasad HK, senior research associate at the research organisation Well Labs. RO water purifiers work on applied pressure, which requires electricity. The pressure forces water through a semi-permeable membrane. This effectively removes dissolved solids like salt and mineral particles as small as 0.1 nanometre (a nanometre is a billionth of a meter).

However, major disadvantages of using these purifiers are that they reject 80% of water for every 20% of filtered water, and also remove essential minerals

The Bureau of Indian Standards (BIS) measures water quality under three broad categories:

  • Physical: Suspended particles, color, smell, turbidity, etc 
  • Chemical: Calcium, magnesium, nitrates, fluorides, iron, etc 
  • Biological: Pathogens like E. coli

While physical and biological elements should mostly be removed, many chemical elements should be consumed in safe amounts. 

Eco-friendly alternatives are available

Instead of RO units, you can opt for environment-friendly purifiers as per your requirement, such as:

  • Ultra-filtration (UF) purifiers: They have a fine membrane to separate and remove microorganisms and suspended solids from water. They waste no water, and don’t require electricity. 
  • Ultraviolet (UV) purifiers: They use ultraviolet (UV) light to disinfect and sterilise water by damaging the DNA of microorganisms, disrupting their replication. UV filters are often used as the final step in water treatment systems to ensure the removal of any remaining microorganisms that may have survived previous filtration stages. Hence, they come with RO, UF or NF purifiers, and not as an independent unit.

Other technologies like nanofiltration (NF), microfiltration (MF) and electro-adsorption technology (EAT) are less popular in the water purifier industry. 

For water with TDS above 300 ppm, RO is essential for both purification and TDS reduction. Below 300 ppm, UF+UV purifiers effectively remove microbial contaminants and Total Suspended Solids (TSS), ensuring basic water purification.

Does your home need an RO purifier?

“When someone approaches for water purifier suggestions, I ask them their source of water first,” says Priyanka Jamwal, Senior Fellow, Water and Society Programme at the research organisation ATREE.

Bengaluru draws its drinking water from two main sources — the Cauvery River and groundwater. Currently, only the city’s core areas receive Cauvery water. “About half the city, mainly in the outer areas, relies on groundwater via borewells and tankers,” says Hari Prasad. 

BIS prescribes the following levels of Total Dissolved Solids (TDS) in drinking water:

  • Desirable level: 500 ppm (parts per million)
  • Permissible level: 1,000 ppm 

However, WHO prescribes 300 ppm as the desirable level. 

Consuming water with high TDS levels can cause chronic health problems like gastrointestinal and cardiovascular issues, increased kidney strain and organ damage.

Water experts point out that the TDS levels of Cauvery water is below 200 ppm, making it ideal for consumption. Though BWSSB treats the water, the distribution system is very vulnerable to sewage, bacteria and groundwater contamination since water supply is intermittent, says Priyanka.

Given the low TDS, Cauvery water can be purified just by boiling, she says. “Boiling water kills most microorganisms, but you would have to boil it everyday before consumption.” Besides, you should consume the boiled water the same day. This is because not all pathogens can be killed with boiling and they may replicate quickly. Hence UV+UF would be the ideal option for purifying Cauvery water, says Priyanka. UF would filter out most microorganisms, and UV can kill the ones that remain.

Those who draw shallow groundwater through open wells, mainly in the core areas of the city, can also use UV+UF units, says Rakshitha ML, project coordinator, Biome Environmental Trust. This is because shallow groundwater too has low TDS levels.


Read more: Is your water safe to consume? Here’s how Bengaluru residents can check water quality


However, when people dig deeper or near contaminated lakes to extract groundwater, especially in the outer parts of the city, the water would have high TDS levels. Such water would have to be purified using RO units. “As you go deep, the water gets mixed with the soil minerals, making them hard and non-potable,” says Shashank Palur, senior hydrologist at Well Labs. Additionally, water quality would depend on the location of extraction. For instance, groundwater extracted from industrial areas like Peenya may contain heavy metals.

Bengaluru lacks geographical mapping of the TDS levels of groundwater in different regions, says Shashank. “We do not even have a proper mapping of groundwater levels in the city, let alone quality mapping. Hence people resolve to RO water purifiers as a silver bullet for all problems.” 

Many even mix their Cauvery water with groundwater because of the intermittent Cauvery supply, and then opt for RO, says Hari Prasad. 

However, consuming water with extremely low TDS can also cause health impacts such as mineral deficiencies and weaknesses. Most brands now check TDS levels before suggesting purifiers, says Srikanth Odi, service technician at Eureka Forbes. You can use a TDS meter to check the levels in your water as well.

Many RO water purifiers also come with a TDS controller which allows the user to set a desirable TDS limit. Setting a higher limit allows users to restore essential minerals in water. RO units also now come with chambers of copper and other essential minerals to add lost minerals to purified water. 

Reject water can be reused

You can use the reject water from your RO unit for many purposes – to clean floors and cars, to water large plants and trees, and to soak vessels with hard stains. But since the water has high TDS levels, it is not suitable for washing clothes or vessels.

“We use the reject RO water twice on most occasions,” says Lalithamba BV, a HSR Layout resident who uses a RO purifier. “We collect and use it to soak vessels and to clean the floor. Also, we use natural dish washer and disinfectant materials, which is why post cleaning we reuse the same water for gardening.”

“Many people think it’s just a little water, what difference does it make? But water is a shared resource. Just because we can afford it, does not give us the right to waste this threatened resource,” says Odette Katrak, environment and sustainability changemaker.  

Odette replaced her RO water purifier with a UV+UF unit six months ago.

water purifier
The UV+UF water purifier at Odette’s home. She has replaced the plastic container in the purifier with a stainless steel tank to store water. Pic: Odette Katrak

She has proposed a framework named ‘Ecowaternomics’, based on the principle of reusing water according to a hierarchy of water needs. Many water needs can be met without fresh or high-quality water.

Water purifier companies are also now coming up with innovative solutions for climate-conscious customers. For example, Aquasave is a product designed to collect RO reject water in a tank for further use like cleaning or gardening. Flow restrictors reduce the water output from RO water purifiers. However, Vinosh says these would reduce the shelf-life of the RO membrane.

Reducing dependency on RO purifiers

“All RO water purifier advertisements tap into the aspects of safety and family well-being. It’s a clever marketing move to convince people, whether or not they require RO,” says Shashank. “Several companies even offer a combination of services which make no sense, like RO+UF+UV+NF. After a thorough RO purification, why would one need UF or NF? Lack of awareness and concern for safety makes people fall for these marketing gimmicks.”

Many sales representatives even push RO purifiers that provide water with 100 ppm TDS levels in homes where no RO is needed.

“People will continue to purchase RO water purifiers unless they are confident that high-quality Cauvery water will be provided regularly and until our aquifers are recharged sufficiently,” says Hari Prasad. He emphasises that rainwater harvesting is crucial today to increase groundwater levels, which would give us access to better quality groundwater.

Also read:

Comments:

  1. vaibhav says:

    Thanks Harshitha, It is very good article. In Bangalore most of places RO are used in multistory building. Height of building can be used to collect water from all flats above ground level and can be reused in bulk. This kind of provision should be there in the BBMP rules. This water has 30% more minerals than source of water. This can be remixed with raw water and it will not harm in any way. Generally Raw water requirement is much higher than potable water.

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