Reverse osmosis

Reverse Osmosis 101: What Does It Remove?

Purified water is always in demand for various purposes, including drinking, manufacturing, beverage industries, medical and pharmaceutical fields, etc. Tap water contains many contaminants making it inadequate for domestic or industrial use. 

For this reason, water purification becomes paramount to help remove these dangerous impurities from the water. But, while there are numerous water purification methods, reverse osmosis is one of the most effective techniques. 

Initially, this method was developed to help turn saltwater into potable drinking water. However, with advancements in technology and growth in industries, reverse osmosis is now mainly used at industrial levels. 

Here, the process is used to filter away various solids, trace metals, and harmful organisms from the water. The purified water at the industrial level is later used chiefly for cooling or heating purposes.

With over 40 percent of Americans using reverse osmosis purified water, it’s only fair to answer this crucial question in detail; what does reverse osmosis remove from tap water? 

But first! 

What is Reverse Osmosis? 

Reverse Osmosis (RO) is typically a water purification process that uses a semi-permeable membrane to eliminate ions, undesirable molecules, and solid particles from water. The purified water is used for domestic or industrial use.

Through the RO process, applied pressure helps overcome the osmotic pressure, forcing a more concentrated liquid through a semi-permeable membrane to a lesser concentrated one.

In essence, it’s osmosis taking place backward, hence, reverse osmosis. Instead of water moving towards a concentrated solute, it moves to a lower solute concentration through applied force. 

The semi-permeable membrane used in reverse osmosis allows water to pass through, trapping back the undesired particles. This brings the impurity levels in the water down to 0.0009 microns, making the purified water safe to drink or use for other purposes. 

At the industrial level, reverse osmosis systems use pressurized containers, especially fit with semipermeable membranes. The pressure that the RO system uses can easily be reverted to the industrial plant, offering an excellent way of reusing power. 

But, precisely what does reverse osmosis remove from water?

The process eliminates many impurities, dissolved and suspended, leaving the water ideal for industrial or domestic use. Let’s take a deeper look.

What does Reverse Osmosis Remove? 

With a pore size of around 0.0001 microns, an RO’s system membrane is quite efficient. So, when you use reverse osmosis, what does it remove?

  • Protozoa – the system is efficient enough to trap back even the tiniest parasites such as Cryptosporidium and Giardia, which would cause diseases when consumed. 
  • Bacteria – reverse osmosis system can also sieve off bacteria, such as Salmonella, E. coli, and Campylobacter, leaving the water clean and potable.
  • Chemical contaminants – mainly metal ions and aqueous salts. These include copper, lead, sodium, and chloride. It also reduces the amount of arsenic, sulfate, calcium, magnesium, mercury, zinc, and potassium in water.
  • Viruses – such as Hepatitis A, Rotavirus, Norovirus, and Enteric. This is due to its effective membrane that removes even some of the tiniest substances. 

The RO process can reach efficacy levels of up to 99% or more. It works perfectly in removing most of the dissolved salts, organics, bacteria, colloids, and pyrogens from water.  

The RO system’s semi-permeable membrane sieves the contaminants contained in water based on size and charge. For instance, a properly functioning RO membrane will reject contaminants greater than 200 MW (molecular weight). Since water molecules weigh around 18 MW, they pass through the membrane while the rest don’t. 

Also, highly ionized particles will be rejected by the membrane. For instance, while sodium ion (one charge), and calcium (two charges), are not eliminated by the membrane, it removes others like arsenic. 

Since the system will not remove gases like CO2 (as they are less charged), purified water’s PH might sometimes be lower. 

Pros of Reverse Osmosis 

  • Clean water with Fewer Contaminants

As the process removes up to 99% of contaminants in tap water, it means that this water is suitable for drinking. Fewer contaminants mean fewer diseases and health issues. 

For instance, reverse osmosis filters off lead molecules from water, protecting people against health issues such as nerve damage, low fertility, and high blood pressure. Also, since it gets rid of parasites and bacteria, it guards your body against contracting various diseases caused by these organisms. 

Therefore, drinking RO purified water translates to healthier living.

  • Improved Taste of Water

While the taste of water is subjective, several studies imply that purified water rates higher than tap water. Various blind water taste tests indicate that many people prefer purified water to tap water. This is mainly because tap water contains traces of lead, nitrates, sulfur, and many other compounds, giving it a different taste.

Therefore, reverse osmosis helps to provide people with clean, fresh, and tastier water.  

  • No Added Chemicals

While other water purification methods might use chemicals, reverse osmosis technology doesn’t. The system merely removes the dissolved and solid particles from the incoming water through applied pressure and a semi-permeable membrane. This means that the process produces water that is safe for your health.

  • Environmentally Friendly

Since RO purified water is an alternative to bottled water, it helps reduce the number of plastic bottles ending up in the environment. 

Cons of Reverse Osmosis 

Even with all the benefits, the process also has some drawbacks. Some of the main ones include:

  • Water wastage – this is the primary drawback of this process. For every gallon of clean water, the system produces between 2 and 20 gallons that go to waste. And, for the large industrial RO systems, disposal of wastewater can become another burden. 
  • Wear and Tear – the system’s membrane is prone to damage and decay, necessitating periodic replacement. This can add to the operational cost of the system. Also, if the membrane is damaged, it will compromise the quality of your purified water. 
  • The RO system doesn’t filter every contaminant from the water. Some contaminants still get through the membrane.
  • Worn-out membranes might allow harmful microorganisms to pass through, leading to health complications. 

What Reverse Osmosis Systems Don’t Remove

While reverse osmosis technology is considered the ultimate solution in water purification, it also has its limits (it’ not 100% effective). The process is unable to completely get rid of some solvents, pesticides, and volatile organic chemicals such as:

  • Dissolved gases like chlorine and Radon
  • Pesticides like Atrazine, 1,2,4-trichlorobenzene, and 2,4-D (dichlorophenoxyacetic acid)
  • Organic chemicals like Carbon tetrachloride, Benzene, and Dichlorobenzene

With considerable amounts of these substances finding their way into the water, it means that reverse osmosis is not enough on its own. 

For this reason, the reverse osmosis water purification method will sometimes necessitate additional technologies to cover all the gaps. Some of these extra technologies might include ultraviolet light, pre- and post-filters, or activated carbon. This way, any contaminant that escapes the RO’s membrane is addressed by another purifier.

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