RO water purifier stands quietly in the kitchen. It makes a slight humming sound. It provides us with clean drinking water. However, have you ever thought about what goes on inside it? Most of us understand the need for a good RO water purifier. We know that it removes “TDS.” But the technology inside seems like a magic box.
The thin layer of material does all the heavy lifting in providing us with good quality drinking water. It converts the salty and hard water into clear and consumable water. Let’s find out more about how it works.
Ready to upgrade? Check our top list: Best RO Water Purifiers in India: Our Top Picks for Your Home, 5 Best Aquaguard Water Purifiers in India: Tested and Reviewed
The Problem with Indian Water
In India, access to clean drinking water is a challenge. You may have access to a municipal water supply or a borewell. Alternatively, you may get water through tankers.
However, the issue with our water supplies goes beyond just seeing particles of dust or dirt in it. We can remove these through using a cloth for filtration. The main concern with water contamination is what we cannot see.
We are referring to dissolved salts, which we know as total dissolved solids (TDS). This gives water a salty or bitter taste. Apart from TDS, there are heavy metals such as lead, arsenic, and mercury. They are very harmful.
Pesticides and other chemicals used in farming can contaminate groundwater too. Besides, bacteria and viruses which cause stomach infections are also present. Boiling water kills bacteria. However, dissolved salts and heavy metals cannot be removed through boiling.
To provide healthy drinking water, you need a strong purification system capable of allowing water molecules to pass through while keeping away all contaminants. The Reverse Osmosis (RO) membrane serves this purpose.
Know how to choose best RO water purifier: How to Choose the Best Water Purifier in India: Ultimate Guide
What is an RO Membrane?
The “RO” refers to “reverse osmosis.” The membrane is the highlight. It is a thin layer made from multiple materials layered together. It is usually rolled up in a cylindrical shape inside your purifier.
You can think of it as an ultra-fine mesh or net (it is called a “sieve”). The holes in this special membrane are extremely small. We are talking incredibly small. The pore size of an RO membrane is 0.0001 microns.
For comparison purposes, a human hair is approximately 70 microns thick, a bacterium is 1-10 microns, and viruses are even smaller in size. The pores of the RO membrane are 1000 times smaller than bacteria.
Only water molecules can pass through. The salts, metals, or dust particles are too big to pass through and are rejected by the membrane.
How Does It Actually Work?
The process involves more than just one easy step. It needs a team effort. The RO membrane is helped by additional elements. Here’s how it works from beginning to end.
The first important fact to know is that RO membranes are not very strong. They have a weak point – chlorine. Chlorine is commonly added to municipal water supplies to eliminate bacteria.
The chlorine can weaken and degrade RO membranes. Therefore, before any water comes into contact with the RO membrane, it passes through prefilters. Typically, these include sediment filters and carbon filters.
The sediment filter removes big particles such as dust, sand, and iron sediments. The carbon filter removes chlorine and bad smells. Only after being cleaned of chlorine can it pass through to the membrane.
This is where the term ‘reverse osmosis’ comes into play.
Water naturally follows a basic rule: it flows from regions of low salt content to areas of high salt content, striving to create a balance. This natural process is known as osmosis.
For example, if you pour salt on a slug, its skin will absorb the salt. The body of the slug loses water in order to dilute the salt absorbed by its skin—a perfect example of osmosis. We want to do the opposite.
Your water purifier comes equipped with a pump that applies high pressure to force the water through the semi-permeable membrane. The small pore size allows only clean water molecules to pass through while keeping contaminants out.
As water flows through the membrane under pressure, it divides into 2 streams. We get permeate (clean and healthy water) and concentrate (water containing impurities).
The permeate is the clear water that passes through the fine pores of the membrane and is stored in a storage tank for drinking purposes. The concentrate (or wastewater) contains all the dissolved solids, heavy metals, and impurities that could not pass through the fine pores and is discharged into the drain.
Yes, RO technology results in “wastage” of water. Many people question why some of the filtered water goes down the drain. However, this ‘waste’ is essential for maintaining the purity of our drinking water.
This excess water acts as a “garbage truck” flushing out the impurities from your water. If this excess water was allowed to be stored in the system, the membrane would become choked immediately.
What Does an RO Membrane Remove?
It removes plenty. It is the ultimate filtration method. High levels of TDS (above 500 ppm) can be reduced to safe levels below 100 ppm.
It removes heavy metals such as lead, arsenic, mercury, and cadmium—substances associated with various diseases. It also removes chemical contaminants from agricultural products, including pesticides.
Although UV treatment is effective against viruses, the RO membrane filters out bacteria and cysts through physical barriers. It provides effective defense much like a wall.
For households that draw their water supply from a bore well or municipal water, an RO membrane is not a luxury item; it is a necessary one.
Related: TDS Value for Drinking Water: Best Range and Recommendations
What Does 75 GPD vs. 100 GPD Mean?
When buying a membrane, you may come across numbers such as 75 GPD or 100 GPD. GPD stands for Gallons Per Day; it indicates how much water a membrane can provide in a day under optimal conditions.
The standard is 75 GPD. It is the most commonly available membrane in India—reliable and reasonably priced. However, its ability to fill up the tank at a moderate pace is a drawback. If you empty the tank completely, it may take anywhere between 30 and 40 minutes to replenish it completely.
Then there is the option of 100 GPD. This membrane provides greater quantities of water compared to the 75-GPD one. It helps in faster tank filling. Large families with 5 or more members who consume good amounts of water may opt for this.
However, it requires slightly higher water pressure. If your current water pressure is low, this membrane may not work efficiently without a booster pump. For a family of 4, 75 GPD is the ideal one. If you live in a joint family with increased usage needs, go for 100 GPD.
Related: Best Kent Water Purifiers in India: Our Top 3 Picks
How Long Does an RO Membrane Last?
The membrane is strong, but it will not last longer. On average, an RO membrane lasts for 18 to 24 months. However, its lifespan depends on the quality of your water supply. If your feed water is clear, with a TDS reading of 300 ppm, the membrane can be replaced after 2 years.
If your feed water contains a lot of impurities, with a TDS reading of 1500 ppm or higher, the membrane will have to work harder. It may become clogged within 12 to 15 months of operation.
So, how do you know when to replace the membrane? Listen to your water. Signs that indicate it’s time to replace the membrane include changes in taste.
Does your drinking water have a salty or flat taste? If yes, it indicates that the membrane pores have been damaged, allowing salts to pass through.
Another indicator is the flow rate. Is the water flowing at a slow trickle? It could mean that the membrane has been blocked by particles.
To find out if the membrane is worn out, check the TDS of the filtered water using a TDS meter. If the TDS of the filtered water is almost the same as that of the feed water, it means the membrane needs to be replaced.
A helpful tip is to never ignore the pre-filters. Replacing the sediment and activated carbon filters every 6 months will help extend the life of the RO membrane. Failing to replace the pre-filters will lead to premature failure of the RO membrane.
Read our full guide on maintenance and replacement schedules: Water Purifier Filter Replacement: When to Change RO, UV & Sediment Filters, Water Purifier Maintenance: Checklists and Guidance.
Common Misconceptions About RO Membranes
A common myth is that reverse osmosis (RO) kills bacteria. It does not. RO is a physical filter. Like a wall stopping a human being, it stops bacteria. Unlike chemical filters, RO does not kill them. That’s why modern water purifiers come equipped with RO + UV. The UV light kills viruses, while the RO membrane removes heavy metals from water.
Another common concern is about acidity levels. Some claim that RO water is acidic and unhealthy. While pure RO water has a slightly acidic nature with a pH level ranging from 6 to 7, it is a natural state.
Several fruits and juices too are acidic. The concern regarding loss of essential minerals through RO water is valid. We have mineralizers to address this issue. All modern water purifiers come equipped with mineral-restoring filters, which add essential calcium and magnesium to filtered water, providing us clean drinking water along with good amounts of essential minerals.
Want to know more: RO vs. UV vs. UF Water Purifiers: Which One is Best for Indian Homes?
Key Takeaways
The RO membrane is a technological achievement. It can convert dirty, salty borewell water into fresh and safe drinking water. It works silently by utilizing only pressure and intelligent design. However, it requires some maintenance efforts from you. You need to replace the pre-filter at regular intervals. You need to check the TDS level periodically. And you need to replace the RO membrane after 2 years. With proper care and maintenance, it will provide clean drinking water.
Frequently Asked Questions (FAQs)
Does the RO membrane remove calcium and magnesium?
Yes, it does. RO systems remove almost all dissolved solids, including necessary minerals. Therefore, many water purifiers come equipped with a mineralizer section to supplement the vital minerals required for good taste and good health.
Can I increase the life of my RO membrane?
Yes, you can. Changing the sediment and activated carbon filters every 6 months will extend the life of the RO membrane. Activated carbon filters absorb dust and chlorine particles that could damage the RO membrane.
Why is my RO purifier wasting so much water?
The reject water is needed to eliminate excess salt content. Every liter of pure water obtained through our RO system generates 2-3 liters of wastewater. Every normal RO system produces some amount of waste water. Eco-friendy and new technologies claim to minimize this ratio.
Is 75 GPD enough for a family of five?
No, 75 GPD might not be enough for a family of 5, as there are several ways we use water, such as filling bottles and glasses. For big families, membranes with high GPD capacity, such as 100 GPD, are recommended.