What does a reverse osmosis system filter out?

The reverse osmosis method has been ruling the water treatment industry with no competition, all due to the efficiency in removing contaminants and the low cost. You can get rid of a wide range of impurities, but what does a reverse osmosis system filter out exactly?

How does reverse osmosis work?

In the natural osmosis process, the components will travel from a high-concentration area to a diluted area until an equilibrium is established.

However, in a reverse osmosis system, we have a membrane for water to pass through. The solution after will be less concentrated than the untreated solution since it contains only small particles that manage to fit the pores.

The filter for a system of this kind features a pore size of 0.0001 μm – enough to let the water molecules pass and hinder every particle that fails to fit.

What can a reverse osmosis system remove?

Based on the principle of the reverse osmosis process, we can tell that the determining factor of which impurities will be gone is not the type of contaminants they are, but the size of the particles.

Here is what you can expect from an RO system:

– Removal of contaminants

– Reduction of odors and abnormal tastes

Unfortunately, beneficial minerals such as sodium, potassium, calcium, and more along with contaminants like arsenic, nitrates, sulfates. It is a fair exchange, for these contaminants might be very harmful to your health.

Nonetheless, the WHO has announced that water filtered by the RO system is not safe for the human body when consumed in a prolonged time. Many people might dislike the taste of RO processed water due to the absence of minerals.

What does the reverse osmosis system NOT remove?

A RO system doesn’t soften the water or remove chlorine for you hence it works most efficiently only if you have water filters with activated carbon.

Contaminants with smaller sizes than the filter pores will escape! We can enumerate some of them: herbicides, dissolved gasses, chlorine, pesticides, fungicides, and certain organic compounds.

Does reverse osmosis remove bacteria and viruses?

We are discussing tap water, which means it has been pretreated at your local plant and is considered safe in terms of microbiology. Furthermore, we can’t control the bacteria forming on the membrane and following the current into our water supply.

When it comes to removing bacteria from water, UV disinfection would be a more effective choice!

Where to install your reverse osmosis system?

Under the kitchen or bathroom sink is the most common spot to install an RO system.

You can also connect it to your refrigerator, basement, or garage for a source of clean water.

An RO system can target a certain area of the house where the water is more likely to be contaminated or salted, yet if you want to use it for the entire place, there needs to be some kind of a pump for water pressure.

Another aspect to look at the issue is the level of contaminants in your water if you need to treat water for the whole house. Hardness at high levels can cling to the membrane and sabotage its function. In this case, you will need more than RO.

Does the RO system waste much water?

In regular filters, the contaminants will be trapped in the system and the cleansed water will continue. Meanwhile, the RO system ejects contaminants in a separate stream considered wastewater and sends the filtered water to your household water supply.

How much water will go down the drain?

You will need 5 – 6 liters of water for 1 liter of filtered water. It sounds like a huge ratio but the so-called wastewater is not exactly wasted. By circulating the brine through the cycle, an RO system can efficiently maintain its inside clean.

Nevertheless, it is everyone’s responsibility to reduce the contaminants and impurities in the environment to save water as well as to keep the RO system in a prime condition.


If you live in an area where water is in shortage or you need a method to decontaminate industrial wastewater, reverse osmosis is amazingly reliable. What does a reverse osmosis system filter out? What will you receive? What shouldn’t you expect from it? Knowing the answers to these questions is the very first step for your successful investment.