Reverse Osmosis. Pros and cons?


Waste water is treated in many ways, one of them being Reverse Osmosis. I have worked in water treatment plants over the years and I am not opposed to the idea of better utilising our water supplies, after all, we all tend to take for granted such resources. Even local councils are starting to recycle water by treating sewerage water and dispensing it back into our town water and, ultimately, our household for showering and drinking.

Reverse Osmosis (R.O.) uses an organic membrane to seperate large ions and molecules such as Iron, Fluoride, lead, from smaller molecules such as H2O. Unlike standard carbon type filtration which allows all the water to pass through treating only specific attributes within the water, R.O systems purify water by forcing it through a semi-permeable membrane. It is a simple process, and one that’s been around for hundreds of years.

Today’s R.O systems use a membrane called poly-amide (PA) membrane. Filtering water at around 0.005 microns, so fine that it can strain salt out of the water, R.O is the only true way to remove all contaminants, bacteria and chemicals from your water. These include Inorganic and Organic

Aluminium Chlorine

Arsenic Herbicides

Barium Pesticides

Cadmium DDT

Calcium Endrin

Chloride Lindane

Chromium III

Aldrin Copper

Benzene Fluoride VOCs

Iron Adrazin

Lead Fluorathene

Magnesium Phenol

Manganese Trihalomethanes

Mercury II T

oxaphene Nitrate Dichloromethane

Potassium Chloroform

Selenium IV


Silver Perchlorethylene


Tannic Acids

Strontium Methoxychlor Sulphate

PCB Zinc

Total Dissolved Solids



It all sounds great right? The perfect system to treat my household water and protect my family?

Well, yes and no. On paper the process of RO is great, however, I have noticed that there are many factors that are not understood when choosing this type of filtration. The purpose of this blog is to simplify and make it easy for you to decide if R.O systems are right for you. These are the typical questions I get asked regularly.

Q. I have heard that R.O water is bad for you?

A. No, R.O water will not harm you. However, due to the nature of the process and it's ability to remove most minerals from water, there are some concerns regarding the lack of good minerals remaining. These minerals are sometimes the very ones your body needs. For example. Iron and Magnesium are essential minerals for your body. To counter this, additional (post) mineral filters are usually added to the system to put back the the minerals you do want in the water while still removing the contaminates. These can include volcanic stone, alkaline cartridges and salt additives. What I find best is to add a few course grains of quality unprocessed salt like Pink Himalayan Sea Salt to your water bottle. This also gives the water a more aesthetically pleasing taste. However, if you have a well balanced diet, it is most likely you are already getting the right minerals you need daily.

Q. If the water is being separated what happens to the waste water?

A. One of the downsides to this process is waste water. On a domestic unit the waste water is connected to the drain plumbing and disposed of. Depending on the quality of the inlet water, you will usually see 10-50% of the water go down the drain. This is of course dependant on the amount of water used daily. On domestic systems, In most cases the volume of water disposed of is not a real concern, but is something you should be aware of.

On some installations I have connected the waste water to a tank to be used as non-potable water. On a larger scale the water can be dehydrated and the minerals used as a by product.

Q. I have heard that R.O water is slow to produce available drinking water on demand?

A. This is true. Unfortunately the process of Reverse Osmosis is slow. This is because the water needs to be forced through such small apertures. To overcome this issue a small, usually 15-20 litre tank, is installed under the sink along side the unit to create a buffer of sorts. On commercial units these tanks can be thousands of litres. The domestic tanks not only store the water for on demand use, they also have an air bladder which acts like a pump to provide pressure to your faucet. If you were to use the system without a reserve tank you would have a very poor flow rate at the tap. Larger units utilise a mechanical pump. With domestic units the head pressure of the town water is usually great enough to overcome the membrane. These units are designed that way. In some instances the inlet pressure from the mains can be weak due to pressure regulators that protect the household from surges. If that is an issue a small pump may be added or included with the system to assist with inlet pressure. So when you choose an R.O system it would be wise to consider how much room you have under the sink. Good time for that clean out hey?

Q. How much maintenance is required yearly with an RO system?

A. Most R.O systems come with a four to six stage filtration process. This includes the following:

1. A sediment filter to capture the heavy solids in the water such as dirt or scale. These filters do not chemically treat the water but provide protection to the filters downstream. Sediment filters are cheap and usually cost between five to twenty dollars. For this reason they are usually changed out every three to six months depending on water quality coming in.

2. Carbon block filter. These are the second stage and are used primarily because the RO membrane does not like or treat chlorine. They are an important stage on RO systems to protect the life of the membrane. The carbon filter is usually changed out with the sediment at a cost of around twenty to forty dollars. There are a variety of carbon filters and the correct choice is crucial to the efficiency of the system.

3. The membrane. This is the work horse of the system as I explained earlier. The membrane can come in many shapes and forms. Depending on the unit purchased they may have different flow rates. Usually seen as 50 to 100 GPD (Gallons Per Day) on domestic units. This references the maximum volume of water produced daily. Of course there are factors to take in to consideration that may change the volume of water produced, for example, pressure reduced by the pre-filters. The membrane can last domestically for 2 years, provided pre-filter maintenance is done periodically. You can also determine the quality of the membrane by using a TDS meter (Total Dissolved Solids) to test the inlet water verses the R.O water outlet to determine the efficiency of the membrane.

4. Post Carbon filter. This is used to capture any remaining contaminants that the membrane may eject and clarify the water. If bacteria was to pass through and enter the tank it may cause the stored water to turn foul. In addition or as an alternative, a UV lamp may be installed to kill off bacteria present.

5. Mineral, salt, alkaline cartridges. These are used to add the good stuff back into the water. An Alkaline cartridge can alter the PH of the water to as you guessed an alkaline state usually between 7.5 and 9.5 PH. Some studies have indicated that this is very good for you due to the way is balances our bodies acidity.

Often i will be called out to service an R.O unit with the complaint being that the water taste is earthy. This is a good indicator that bacteria has entered the tank or the system lines and has not been cleaned out during its last major service.

Removal of chemicals in the filtration process such as chlorine and fluoride that are used to protect water from bacteria, will leave the water in an unprotected state post membrane. This is why it is important to have a post filter and/or UV lamp to kill off any remaining bacteria before it enters the tank. Additionally, during annual maintenance a special solution is pumped into the tank and rinsed to ensure it is free from bacteria.

Q. Are R.O units expensive?

A. That depends on a few factors. First off you need to ask how much water will be needed daily for yourself, the family or the whole building. If it is just at home and 15-20 litres per day is enough, then the cost is around $500-$1000. The maintenance is fairly cost-efficient and relatively easy if you are somewhat savvy with basic hand tools.

If you were looking to treat your whole house or treat bore water for household use. Then you would probably looking at around 2000 litres per day. The costs are upward of $7000. However, if it is a bore you are treating then the larger costs involved to maintaining these commercial units could pay off, shaving all those dollars from your water bill.

The larger units will mostly require a trade technician to maintain.


You have heard a few negative points regarding R.O systems, however these are greatly outweighed by the positives. I personally use R.O within my household because it is an additional layer of defence which I can personally maintain to ensure my family consumes safe water. Plus the taste is much better than any over priced bottle of water. Within my business of water treatment I have heard countless stories of how clients healths have improved. To be clear, there is nothing really wrong with the town water we have - it may taste horrible but it won't hurt you, short term anyway. The use of chlorine and fluoride has its purpose in the transportation to your tap, however when it gets to your place there really is no need to consume those chemicals and your body, long term will thank you for it. I have clients that live in rural areas where drilling and fracking have upset their water supply. There are remote places in Australia where the water is just horrible and the use of tank water is common practice. But, if it does not rain then what? RO treatment is the best way to deal with foul water issues in these area.

So, yes, I would recommend RO water treatment if your concerns are health related. If your not in a rural area then standard carbon filtration may be all you need to help the taste. Ultimately the use of consumable water bottles are killing this planet and we all only have one planet to live on. I try to encourage people to use filtration at home and do away with bottled water. There are many companies like my own with very skilled people that can assist you in making the right choices. With the current technology surrounding water treatment, you can most likely have the water aesthetically to your liking.

Hope this helps and thanks for reading. For further questions or advice feel free to contact me.

Ben Wilson

Filtered Fresh