Reverse Osmosis Systems
Why Reverse Osmosis (R/O)?
Reverse Osmosis water purifiers are the optimum system for removal of contaminants from water as they filter down to an ionic level of 0.001 microns. Not only are they very efficient at removing a wide range of chemicals, heavy metals, bad taste and odour, but they will also remove fluoride, bacteria and all the ‘dissolved solids’ from the water which normal water purifiers will not remove. ( ‘Dissolved solids’ are mostly minerals which are dissolved into (or attached to) the water molecule. The main ones in urban treated water being Calcium from lime added to the water along with fluoride which is added to some water supplies to strengthen teeth).
Typically urban treated water contains around 90 to 120 parts per million ( PPM ) of dissolved solids. After passing a standard carbon based water purifier the Total Dissolved Solids ( TDS ) reading will not have changed. After passing a reverse osmosis membrane the reading will drop around 95 to 98 %. Consequentially the texture of the water has a slightly smoother, silky feel to it compared with non R/O water.
In contrast to distilled water, which is often referred to as ‘dead water’, Reverse Osmosis water retains oxygen and has a sweeter, more pleasant taste.
How do they work?
After passing at least one pre filter to remove sediment and usually chorine, the water passes over a semi permeable membrane. The water pressure pushes the pure water molecule through the membrane while the waste product is discharged into the kitchen waste pipe. For every 10 litres of pure water processed, approximately 25 litres goes down the drain. Although this sounds wasteful, it is around the same as running a standard ‘low flow’ shower for only two minutes.
Because the RO membrane is slow to produce pure water ( between 3 to 6 litres per hour depending on available water pressure) the system is normally installed under the sink and is linked to a storage tank ( usually 10 to 12 litres capacity ), which holds the pure water until required. This water is accessed by simply turning on your dispensing tap as the water is required and the system automatically refills the storage tank as water is used.
Some people want portable units. We do not recommend portable systems are connected to kitchen mixer taps as the tap seals will be damaged with the water pressure build up, so portable systems are normally installed in the laundry and connected to the washing machine tap fitting. These usually do not use a storage tank and a flexible feed tube which is placed into a jug or container of the client’s choice and the system is manually turned on and off as required.
Systems usually consist of at least a three stages,-
- Sediment and chlorine reduction
- The RO membrane
- A post carbon polishing cartridge after the storage tank.
The most common is a four stage system with separate sediment and chorine reduction filters although in areas of known dirty water a fifth stage can be added to help remove the sediment.
Extra filters sometimes added to RO systems
- pH balancing cartridge – RO water is very pure and so does not actually accurately read a pH. Some people add a calcite cartridge as a post filter to raise the alkalinity.
- Re mineralizing cartridge - Adds a mix of minerals back into the water with an aim to also raise the pH to an alkaline level.
- De ionizing cartridge – For laboratory or Tropical Fish use, a demineralizing cartridge will remove any remaining minerals and provide absolutely pure water.
Pre filters ( the filters prior to the membrane ) are usually replaced every 12 months depending on the quality of the feed water and amount of use, while the post filter ( the filter after the membrane ) is usually replaced with the membrane every 2-3 years, making R/O systems very economical to maintain. Where chlorine is not present, membranes can last up to 7 or 8 years before needing to be replaced.
The performance of the membrane is determined by using a digital metre to measure the TDS ( total dissolved solids) level of the water to compare the incoming and the treated water. These metres are readily available from only $50.00 or you can give us a sample to test free of charge.
Standard systems compared to the Pentair Evolution system
Whereas a standard RO system has the volume of water limited by the size of the storage tank, the Evolution system will produce a constant 1.7 litre per minute of pure water per minute ( at a water pressure of 600 kpa), so has the advantage that water will always be available. This is ideal for high use situations, but for a domestic home, a standard RO system will produce a better flow at around 2.0 to 2.5 litres per minute and are easier to plumb into a kitchen cupboard.
Water Pressure Requirements
As RO systems use water pressure to push the pure water through the membrane, we require good pressure for effective operation. A minimum of 50 psi (350kpa) is required with an ideal pressure being around 80 psi ( 600 kpa). Most town supply and rural pump supply setups will be adequate but if on a low pressure gravity feed water supply, a booster pump will be required
If you are not sure which R/O system will be best for you, please contact us to determine the best system for your requirements.