Reverse Osmosis Systems

A revers osmosis systemThe vast majority (if not all) of the bottled purified water is treated via a system known as Reverse Osmosis. This is one of the most essential technologies that keep our entire world and every society up and running as it is the preferred technology for treating and purifying water, the most important service and public utility.

The Osmosis as a natural phenomenon has been observed for centuries (since 1748 in France) but the process of Reverse Osmosis filtration is a relatively new technology invented in 1949 in the United States but was impractical: the first Reverse Osmosis system had a very low pressure, consumed a lot of energy and was very big. It was only in 1963 that a synthetic membrane (the screen that filters the water in this system) was invented, allowing its widespread and affordable use; and so, in 1977, Cape Coral in Florida became the first municipality in the world to use this system to purify its water.

Today Reverse Osmosis is widely used in the whole world, and has become like a standard in today’s industry with systems of this type are used in virtually anything that requires purifying water; it is so powerful it is the system of choice for desalinating seawater.

It has also become a viable option for homeowners that want to improve the quality of the water they use for cooking, washing or drinking.

So let’s first take a look at the basic mechanisms behind this fascinating and incredibly useful technology.


So, how does Reverse Osmosis works?

To understand how the Reverse Osmosis filtration works, first, you need to understand Osmosis is a chemical phenomenon in which a fluid flows from an area with few dissolved particles to another area with more dissolved particles, flowing through a semi permeable membrane.

But now imagine this: you have a container full of water that is divided into two sections, those sections are separated by a barrier with small holes; that barrier is called a membrane. Since the water molecules (H2O) are very small, they can cross through the pores of the membrane, but everything else can’t, so dust, garbage, bacteria and even viruses can’t cross, just the water.

The container has dirty water in one half and clean water in the other half. If allowed to flow naturally, then the clean water will flow from its part of the container and accumulate in the half filled with dirty water, since the fluid is attracted towards the part of the container that has the most particles dissolved; which in this case is the half filled with dirty water.

A graphic of schematic process of osmosis

On your left is the container at the beginning of the process and on your is the container after the process of Osmosis process has begun. The red dashed line represents the semi permeable membrane and the purple dots are the dissolved particles.

The Reverse Osmosis system does just what the name implies: it reverses the Osmosis process; so dirty water flows through the semi permeable membrane which stops all the dissolved particles.

To achieve this effect, the Reverse Osmosis system must apply a lot of pressure to the water, so as to overcome its natural osmotic flow and make it work backwards.

Take a look at the following image which represents how the Reverse Osmosis system flows, using the same container used for the above picture.

A second image of the process of reverse osmosis

On your left is the container at the beginning of the process and on your is the container after the process of Osmosis process has begun. The red dashed line represents the semi permeable membrane and the purple dots are the dissolved particles.

After a while though, the membrane that filters the particles may eventually get clogged, to deal with this the reverse osmosis systems have a function called backwash to clean the membranes.

To do it the device simply reverses its flow, and the water flowing backwards dislodges the particles the membrane trapped.

A picture of a backwashing process

The first picture (on your right) shows a membrane that is essentially clogged with all the particles it has trapped. In the second one (on your left) the backwash process has begun: the reverse osmosis system reverses its flow, dislodges all the particles and carries them away.

The water used for backwashing has all the particles the membrane has trapped during an extended period of time concentrated and dissolved in it so it may look like regular water but its taste tends to be displeasing. Such waste water is useless and is usually simply thrown down the drain.


What should I know before buying a home Reverse Osmosis system?

We have seen how this powerful technology works and how useful it can be, and we also know it is commercially available for home users, but before even considering buying a Reverse Osmosis system for your home, you should first answer the following questions to yourself:

  1. What is the quality of the water your home receives?

This is perhaps the most basic and essential question anyone who wants to buy a home Reverse Osmosis system must answer as it will tell you what is the type of equipment you need, what are the capabilities it should have to satisfy your needs or if you need one at all.

To determine the quality of the water you receive at your home you can go to your municipal water utilities supplier and ask for an analysis which is (commonly) done free of charge. Keep in mind that if you want a more complete and comprehensive test with more information such as the level of fecal coliform bacteria or dissolved solids then you are going to need an independent certified laboratory to perform a test.


  1. How much water does your household consumes?

To determine the capacity and size that must have the equipment you want to acquire you are going to need to determine obviously how much water does your household consumes. This amount will vary depending on the number of people that live in your house, and a house with 1 to 3 persons is considered a small household; a house with 4 persons is considered a medium sized household and more than 4 persons is a big household.


  1. How big is your budget?

And finally, you need to calculate how much you are willing to spend. The costs will vary in function of the size of the equipment you need but you can find some basic equipments at prices as low as $130 USD with the biggest ones costing up to $2,000. You should also include the costs of maintenance and services (you are going to need to replace your membranes and perhaps some filter cartridges at some point, and periodically buy salt if you also get a water softener). And do not forget to include the cost of installation in case you are not willing to do that yourself.

Keep in mind that, by some estimates, with a good Reverse Osmosis system, you can save up to a $100 USD per month, so in the long run, a Reverse Osmosis system should pay itself.


Now, the most basic Reverse Osmosis system will have just that: a Reverse Osmosis filter, its pump and perhaps a sediment filter, but a more complete option will be necessary if the quality of your are is too low or if you have the budget to acquire it (as you may imagine, a more comprehensive system is preferable and better) and do not think that a bigger system means it will take much more space, as even the most complete system should fit under your sink.A reverse osmosis water softener system

The addiotonal features or other stages a more complete Reverse Osmosis system may, and maybe also must, include (besides the Reverse Osmosis itself of course) and which you should try to get too if your budget allows it or if you are looking for something other than the most basic system, are:

  • A Sediment Filter. As you may already know, a sediment is a heavy particle carried by a fluid, which tends to sink to the lowest parts of the same when the fluid becomes static. A Sediment filter is like a strainer that will sift these heavy particles, but only those, and will not work with smaller pollutants such as chemicals, bacteria or heavy metals.

Sediment filters are rated in microns, and there are two types: nominal and absolutes filters and they differ in their efficacy. For example, a Nominal 10 micron filter will catch around 85% of all the 10 micron particles (or larger). An absolute filter, on the other hand, is much more effective and will catch a 99.9% or all of the particles of 10 microns or larger.


  • A UV stage. Ultraviolet rays are powerful disinfectants, if a DNA molecule comes into contact with a UV ray, it will be destroyed. All the known living beings have DNA so UV light will kill anything: bacteria, fungi, viruses, parasites, etc.

In nature, UV light comes from the sun, but the Ozone layer stops it, however, in places where the Ozone layer is thinner they may get through and potentially cause skin burns and skin cancer (by damaging the skin cells’ DNA).


  • An Ozone generator. The Oxygen we breathe is composed of two single Oxygen atoms, and so its chemical formula is O2. Ozone, on the other hand, is composed of three Oxygen atoms and so its chemical formula is O3 and in nature, Ozone is formed when a lightning strikes.

Most commercial and home Ozone generators create Ozone by sending the Oxygen in the air through an electric field and then inject the bubbles in the water. Ozone is a powerful disinfectant and it works essentially by ‘burning’ anything it touches: it is a very powerful and unstable oxidizer. So it works much like Chlorine, except Ozone is a 50% more potent than Chlorine and Ozone leaves no traces in the water it treats: it has no taste and it has no smell, and as soon as the water treated with Ozone comes out of a faucet, the Ozone evaporates or disintegrates into regular Oxygen molecules.


  • An Activated Carbon filter. This is a form of charcoal that comes in small pellets, but otherwise looks and feels like regular charcoal (like the one used for barbeques). An Activated Carbon filter holds thousands of pellets and each pellet of Activated Carbon has millions of small pores, this means that each pellet has a pretty large area of contact through which it can interact when water fills the filter cartridge. In fact, just one gram of Activated Carbon has an area of 500m2 or 5,400 sq ft. The Activated Carbon essentially absorbs all the unwanted smells and tastes the water may have, it especially gets rid of Chlorine, but it will get rid of up to a 99% of any smell or taste the water may have.

Almost every home water purification system includes one, although many manufacturers include at least two in all their models; one regular filter and one post carbon filter just to guarantee the quality and taste of the water.


Best reviewed home Reverse Osmosis systems

Finally, and for your future reference, here is a compiled list of the models of Reverse Osmosis systems considered the best by the users, along with their most important features and prices (all data as of 2015):

  APEC High-Flow 90 GDP APEC Countertop iSpring 75 GPD 5 Stage iSpring 75 GDP 6 Stage Home Master Full Contact
Size (inches) 16 x 5.2 x 17.5 15 x 7 x 18 14 x 6 x 6.5 15 x 8 x 18 20 x 16 x 13
Filter life 12 months 12 months 12 months 6-12 months 12 months
Price $299.35 $229.00 $198.99 $229.50 $349.99
Warranty 1 years 1 years 1 years 1 years 5 years
Users rating  4.7 Stars  4.8 Stars  4.5 Stars  4.3 Stars  5 Stars



In conclusion, if you are unsure about the quality and hardness of the water at your home or if you would just like to ensure it, then a home Reverse Osmosis system might be just what you need, but it can be a considerable investment (despite being one that may potentially recover its cost for you in time) and as such, it has to be done carefully, determining your needs and the needs of your household and which of all the models offered better fulfills such needs and demands.