The Definitive Guide To Reverse Osmosis
The Definitive Guide To Reverse Osmosis

We all know reverse osmosis (RO) helps turn unusable water into water that we, our pets, and our plants can enjoy. But have you ever wondered what the process of reverse osmosis is? It’s more than just a filter because a Brita water filter doesn’t do the work a Nu Aqua 5 Stage RO system will.

That’s why we’re going to take you through the in’s and out’s of a reverse osmosis system. Whether you want pure, clean drinking water or you need a highly efficient water softener, we’ll show you how RO systems work to give you the clean water you, your plants, and your pets need.

Osmosis and Reverse Osmosis

Osmosis-ColorTo understand what reverse osmosis is, it’s important to know what osmosis is. Osmosis is a natural process where a solvent (like water) with a low concentration of solute (like salt) will try to find equilibrium between itself and a solvent with a high solute concentration by passing through a semi-permeable membrane from low concentration to high.

That’s the scientific answer, anyways. Here’s a much easier way to explain it:

Take a u-shaped tube and put a semi-permeable membrane (like a filter) in the middle. Then fill one side with water that has a lot of salt in it, and the other side with clean water relatively free of salt. Osmosis will make the water without salt flow into the source of water with lots of salt to balance everything out.

In the process of osmosis, the goal for the solvent (water in this case) is to find a balance between its low-concentrated self and the more concentrated solution.

Reverse-Osmosis-ColorEssentially, one side without solutes wants to be the one with them, so it will pass through the membrane to get what it wants. Our kidneys do the same thing when extracting water from our blood, and plants use osmosis to absorb water from soil: they all absorb what they need from the source without taking in elements (like red blood cells or dirt) it cannot break down.

So then reverse osmosis is– you guessed it- that process in reverse. That means instead of allowing a solution like pure water to naturally find its way to a source of water with a high concentration of salt, we’re unnaturally forcing water with lots of salts (and other elements) through that same membrane and not allowing those elements to come through. What’s left is water that has very few solids in it.

Now that we’ve got the theory out of the way, let’s talk about how reverse osmosis is performed. All we need for that are water and semi-permeable membranes.

Semi-Permeable Membranes and Filters

ro membraneWe’ve mentioned them quite a bit already, so we want to take a step back and explain what a semi-permeable membrane is. A semi-permeable membrane is a membrane that lets certain molecules and atoms to pass through it while blocking others.

Think of a screen door: oxygen molecules and water vapor can come through the tiny pores in the screen, but bugs can’t. In the same way, the membranes in an RO system allow water molecules to pass through them while keeping elements like lead, sediments, chlorine, and mercury out of the result.

RO systems send water through a series of filters and membranes to give you the delicious tasting water you’re looking for. The NU Aqua Platinum Series 5 Stage 100GPD RO System, for example, passes water through 5 filters before it’s ready for use:

Sediment FilterThis is the pre-filter stage which is designed to strain out silt, dirt, and other sediments. This stage is especially important because the sediment filter prevents dirt from getting into the RO membranes, which can be easily damaged by sediments.

Carbon Filter- This filter is designed to eliminate chlorine and all other contaminants that can affect the life and performance of the RO membrane. Additionally, the carbon filter improves both the odor and taste of water.

5_stage_system_only_3-minReverse Osmosis Membrane- This is a semi-permeable RO membrane in the reverse osmosis system that is specially designed to allow water through. However, the RO membrane also filters out other water contaminants.

Note: There are some things that membranes won’t filter out. Particularly, viruses and bacteria. While harmful elements like arsenic and pesticides can be scrubbed out of your water, microorganisms like bacteria and viruses found in well water will not be filtered out. Microorganisms need to be treated before you can use them, so keep this in mind when sourcing your water and your RO system.

Polishing filter- This is the final filter which polishes off the water and removes any remaining odor and taste in the water. This filter also ensures that the water is clean and safe to drink.

Upkeep and Pretreatment

While RO systems will get rid of lots of the molecules it filters by sending them down a drain, it’s still vital to make sure you clean and treat membranes regularly. Without upkeeping membranes and filters you can severely damage the entire reverse osmosis system. Worse, you could send unwanted particulates right back into your good water. Here are just a few issues that reverse osmosis systems experience when all those unwanted molecules are sent through those membranes:


FO-and-RO-fouling-e1402647976626A fancy word for “plugging up”, a membrane will foul out an RO system pretty fast if not addressed. Interestingly enough, it’s not the pebbles and large molecules that foul membranes. Things like silt (really fine dirt), humic/fulvic acids, and bacteria fill hit the front end of your membranes, clog them, and decrease water quality and pressure.


Just like bathroom scaling, RO scaling happens when dissolved compounds like calcium and salt build-up and come together in scale-looking growth. When scaling happens, compounds like salt will pass through filters easier, resulting in lower quality water. Moreover, with scaling, you’ll get smaller amounts of clean water and lower water pressure.


In terms of scaling and fouling, there are one of two solutions to fixing the issue:

  • Cleaning: From simply cleaning of membranes with soap and water to hardcore cleaning with bleach, a good scrub down and rinse of membranes and filters will stop a lot of scaling and fouling on membranes.
  • Replacement: Eventually, membranes and filters will start to wear and their pores won’t stop molecules and atoms like they used to. When cleaning just won’t do the job anymore, it’s time to replace the membrane altogether. When that’s the case, you can check out our replacement filters and membranes for a quick, easy fix.

Chemical Attack

chemical attackWhile it’s not too common, chemicals can overwhelm membranes resulting in chemical burning. This happens when the concentration of chemicals/molecules being forced through the membrane is too high or incompatible with the filter. High amounts of chlorine, for example, can “burn” the holes of a membrane and causing irreparable damage the entire filter. When that happens, water will flow through the membrane with little to no filtration, resulting in low-quality water (though an oddly high water flow rate).

As for chemical attacks, there’s little you can do after a chemical burn other than replacing the membrane itself. You can, however, assure that chemical attacks don’t occur.

  • Make sure the membranes of an RO system are compatible with the water you’re forcing through it. If you’re forcing chemicals through a system that can’t handle it, you’re just asking for trouble.

Benefits of Reverse Osmosis

If you’re planning to get a water filtration system that will give you clean and safe water, here are some of the reasons you should consider an RO system:

It is simple to maintain
Reverse osmosis systems have few moving and replaceable parts, which makes it easy to service the system.

Improves the taste of water
The RO system filtration stages help remove odor and enhance the taste and appearance of water. Through the four filtration stages, contaminants that cause odor and taste problems are eliminated.

Is sustainable and affordable
By investing in an RO system, you will no longer need water delivery services. This means that you won't need bottled water. Although bottled water is often purified through a reverse osmosis system, producing bottled water will waste more water compared to a reverse osmosis system. A lot of water is needed to make a single bottle of water.

During the water purification process of bottled water, wastewater is channeled to the drain. Additionally, water and petroleum are used as raw materials in the production of bottles. Afterward, petroleum is used again to deliver bottled water to stores. Not to mention, the trucks that deliver the water will require a lot of water themselves for cleaning. These little details make reverse osmosis all the more appealing to the avid environmentalist.

Removes impurities
There are very few filtration systems that can remove all water contaminants. But reverse osmosis has been found to eliminate most of the dangerous water impurities. RO removes all contaminants and what is left is clean and delicious drinking water. Some of the impurities it can remove include:

  • Fluoride
  • Lead
  • Chlorine and Chloramine
  • Detergents
  • Nitrates and sulfates
  • Mercury
  • Bacteria


Why Reverse Osmosis is Better Than Other Filtration Methods

Although there are several other water filtration options, including faucet filters, refrigerator filters, and pitcher filters, very few can help reduce dangerous and invisible contaminants or even improve the taste and smell of the water. A reverse osmosis system can remove dangerous contaminants that other filtration methods cannot. Additionally, most refrigerator, pitcher, and faucet filters often require ongoing and expensive maintenance for continued optimum performance.

RO Systems vs. Water Softeners

Unlike an RO system, using a water softener won’t filter out contaminants from your water. Instead, it will only remove magnesium and calcium to soften the hard water and make showering and washing clothes easier.
Reverse osmosis softens water. However, using your RO system to soften or treat hard water will shorten the life of the reverse osmosis membrane, which will lead to frequent membrane replacements. Therefore, if you have hard water, it’s advisable to install a water softener before the reverse osmosis system to remove iron from the water which can stain your clothes, shower, and clog your RO membrane. The RO system will then remove the water softener.


NU Aqua

NU Aqua

@John Cologgi: The semi-permeable membrane functions by selectively allowing certain molecules and atoms to pass, just like a screen door that permits the flow of oxygen and water vapor while keeping out larger entities like bugs. In this analogy, the “bugs” represent undesired elements such as sediments and VOCs, which are effectively blocked by the membrane’s fine pores.

NU Aqua

NU Aqua

@walter: Our Platinum Series 7 Stage RO System features a waste to water ratio of 3:1 or 2:1, depending on major factors like the water pressure and source, meaning it generates 1 gallon of filtered water from every 2 or 3 gallons of waste water.

John Cologgi

John Cologgi

You say the RO membrane won’t remove biologicals. Bacteria run down to about 0.3 micron, virus down to 0.05 micron and an RO membrane filters down several orders of magnitude smaller, so how do the bugs get through?



how much water is used to get 1 gal of reverse osmoses water using your 7stage system

Leave a comment

All comments are moderated before being published