Reverse Osmosis Systems

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What does a reverse osmosis water system do?

Reverse osmosis is the process of liquids within the same system trying to reach equilibrium, meaning the same concentration of contaminants, on both sides of a barrier or membrane. Placing a membrane between two compartments in a container and then placing salt water in one half of the container and pure water in the other half allows the pure water to pass through the membrane to the saltwater side. Essentially, a reverse osmosis system produces pure water by filtering out the salts and other contaminants. Reverse osmosis membranes reject almost all bacteria and particles, making a reverse osmosis water filter one of the most advanced on the market. 

System, Design and Operation

Water Pressure

All reverse osmosis (RO) systems require pressure to operate. Variations in pressure either too high or low can cause changes in water quality from the unit. RO systems can operate with a minimum pressure of 280kPa although 400kPa is more ideal. Systems should also be limited so that they do not exceed the maximum 865kPa operating pressure. This is normally done with a 600kPa pressure limiting valve and keeps the units in the ideal operating range of 400-700kPa. A water pressure gauge on the RO System is beneficial to confirm the available water pressure after installation and during the life of the system. A small 12 or 24 volt boost pump will be required for systems installed in low pressure areas.

Pure Water Production

The volume of water produced varies depending upon the water pressure, the membrane capacity and type. Aqua Safe only use Dow Filmtec TFC (Thin Film Composite) membranes with 400 litre/day membrane capacity. Solute rejection rates for these membranes are listed below under Performance Specification. Pure water production is generally 8-10 litres per hour which equates to 2-3 minutes to fill a glass. Due to the slow water purification process, the ASBTRO4 bench top portable unit, needs to fill a jug or storage container so water is available when required. The ASRO4 under bench RO System has its own water storage tank available in various sizes to provide water on demand.

Waste water

All RO units produce waste water as part of the purification process. This is necessary to constantly clean the membrane and remove contaminants. Without this the quality of water produced is poor and the life of the membrane will be short. The amount of water going to drain or waste is called the waste ratio. This can be as high as 1:6 (1 litre produced to every 6 litres wasted) or as low as 1:1 -1:1.5. Below this ratio the water quality will be reduced at an exponential rate to a point where the water quality entering the membrane is the same quality as the water produced. The filtered water quality coming out of the RO System should have a TDS (Total Dissolved Solids) under 10ppm with an average of 5-7. The waste water coming from a RO System does not need to be put down the drain, it can be used on the garden or lawn instead. Contact Aqua Safe for options and fittings for this.

pH of Reverse Osmosis Water

The more pure water is the lower the pH or the more acidic it is. Town water is generally between 7 and 7.3 which is considered balanced. The water produced by a good quality standard RO System will generally be around 6.5 to 6.8, slightly acidic. If further purified and de-ionised it will lower to 4.5 – 5.8. Ultrapure water actually comes out of the system at a pH of 7.0 however as soon as it comes in contact with air it rapidly picks up contaminants such as carbon dioxide (CO2). The carbon dioxide in contact with water changes to carbonic acid which then quickly lowers the pH. A pH of 7 or more is desirable for long term human consumption. To do this customers can add a pH balancing cartridge, raising the pH to approximately 7.3 or a re-mineraliser cartridge or Pi filter that will raise the pH to 8-9 by adding calcium and trace elements.

Membrane life

Membrane life is affected by water quality and RO System maintenance; how often the filters are changed. This is particularly important with the carbon pre-filter. This removes chlorine from the water supply and is essential to protect TFC membranes. Chlorine and chloramine attacks TFC membranes resulting in premature failure. Poor quality water caused by high hardness, colloidal clay, iron and other contaminants without sufficient pre-treatment will quickly block and destroy the membrane.A well designed and maintained system should enable a 3-5 year membrane life or more. An optional total dissolved solids (TDS) meter can be installed on the system to monitor membrane quality and alarm when the water quality goes below specification. This allows the membrane to be changed when required rather than a predetermined date. It will also let you know if for any reason it should fail prematurely.

How much does a reverse osmosis water system cost?

A reverse osmosis water filter can vary in price, but the cheapest models usually begin at $200. However, it’s important to ensure you purchase a quality system with a highly rated membrane, which is likely to cost between $500 -$1000 depending on the model. Reverse osmosis filters also require additional costs like replacement cartridges, which are usually around $50 each. The annual service cost for the system is approximately $100 per annum for a three or four-stage system for the pre-filters and the cost of any ancillary filter or membrane that may need replacement at the time.

How much water does a reverse osmosis system waste? 

A reverse osmosis water filter doesn’t waste water but rather uses it to create the level of pressure required for the reverse osmosis process. The leftover water from the process can serve various purposes around the home, from watering plants to cleaning dishes and mopping floors. 

The Water Filtration Stages/Process

Reverse Osmosis Filtration Systems have multiple filters and stages of filtration 3, 4 or 5 stage systems are the most common with 4 and 5 stage systems that most popular for drinking water purposes. Standard 4 stage systems such as our ASRO4 start with a sediment filter followed by a carbon filter, the membrane and a further carbon filter or two carbon filters for 5 stage systems.Additional re-mineraliser or Pi filters can then be added to provide the desired water quality. Specialised cartridges can also be optioned to pH balance, produce alkaline water, further purify the water or protect the membrane against hard water. RO systems produce or filter the water slowly (8-10 litres/hour) leading to the final process of storing the water in a container or tank. Due to the design of the Aqua Safe System, the storage tank can be located away from the system, in another cupboard or under the house, saving room while providing more flexibility. Benchtop RO Systems are portable and therefore somewhat manual in operation. They need to be turned on when water is required and turned off when the storage container is full. Underbench RO Systems are automatic in operation, when a certain amount of water is used from the storage tank, the RO System starts operating to refill and replace the water used. It uses no power just town water pressure.

Reverse Osmosis Water System Components

The main difference between reverse osmosis units on the market is, the design of the system and quality of the components used. Aqua Safe Systems use American made NSF certified materials or certified to the applicable NSF/ ANSI Standard 42, 51, 53, 58 or 61. (Contact Aqua Safe on or call 1300 661 735 for details on manufacturer & certification) filters. We only use genuine John Guest fittings and tube. The membranes are Dow Filmtec TFC made in the USA. The other critical components are the high quality dual check pressure limiting valve made by Apex in New Zealand and the USA manufactured Payne auto shut off valve. We have selected these components because we, like our customers expect trouble free operation for longer than the 10 year warranty we offer. Our experience gained over 25 years in the water treatment industry has proven that quality and service leads to happy customers.

Our Difference

Aqua Safe International has been in business for over 20 years with senior management having over 25 years experience in the water treatment industry. We were the first water filtration company to offer a 10 year warranty in Australia (7 years more than our competitors at the time) and the first to offer an unconditional no questions asked satisfaction guarantee without all the exclusions and fine print. We are able to offer these warranties and guarantees because of the quality components we use. We only have premium systems rather than different quality ranges, this gives ourselves and our customers peace of mind knowing there are not going to be issues or problems with the product or system. We can install and service your system anywhere in Australia at a fixed price if you are unable to do it yourself. No need to find a plumber, just leave it to us. We will do it all for you. The filter cartridges we use along with many components are NSF certified materials or certified to the applicable NSF/ ANSI Standard 42, 51, 53, 58 or 61. (Contact Aqua Safe on or call 1300 661 735 for details on manufacturer & certification) providing performance you can trust. The water supply or mains connection kits supplied with all our systems are fully compliant in all states of Australia. The design of our systems (particularly reverse osmosis) comes from experience with supply, installation, commissioning and operation of commercial systems. These systems are generally more complex however the fundamentals are the same and many features can be included in residential systems.

Reverse Osmosis Comparison Table

System Town Water Filtered ASBTRO4 ASRO4 ASRO4R
Fluoride Removal Percentage (As tested) 96% 96% 99.99%
Water Purity (Megohms) (Ultrapure Water = 18.2 – 20 Megohms) 0.001-0.01 0.2-1.0 12 12 18.2
System Technoloy Membrane & Carbon Membrane & Carbon Membrane Carbon & Resin
Filter Location Under Bench Under Bench Under Bench
Micron Rating 0.0005 0.0005 0.0005
Sediment Removal
Chlorine Removal
Chloramine Removal
Trihalomethanes (THM's)
Volitile Organic Compounds
Heavy Metals
Minerals Some Some
Bisphenol A (BPA)
Endocrine Distrupting Chemicals (EDC's)
Taste & Odour
Cartridge Life 12 months 12 months 12 months
Filtered Water pH* 6.5 - 6.8 6.5 - 6.8 5.8**
pH Balancing Cartridge Option*
Remineraliser Cartridge Option
Water Available on Demand
Water Wastage
Water Wastage / Day Average 3-4 litres 3-4 litres 3-4 litres
Unit Cost $240.00 $685.00 $943.00
Operating Cost / Year $49.00 $46.00 $52.00
* pH dependent upon incoming water supply. ** Pure Water (12 has an approximate pH of 6.8 while UltraPure Water (18.18 has an approximate pH of 7.0 when not exposed to the atmosphere.

Reverse Osmosis Systems

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