Reverse Osmosis Water Filter Systems
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Reverse Osmosis is the ultimate filtration method, separating water molecules to produce pure drinking water and waste water, which contains all the eliminated contaminants.
Whilst chlorine and other chemicals can be removed by carbon filtration, it is the ultra fine Reverse Osmosis membrane, filtering down to .0001 of a micron, that ensures only pure water is produced, without Fluoride.
With so many configurations on the market it is not surprising that consumers can become overwhelmed by what is on offer. I regularly get asked the benefits of a 5, 6, or even 7 stage systems. The facts are, the main component of reverse osmosis is the membrane which separates water into pure and waste water. Other stages simply facilitate the removal of sediment, chlorine and, in some cases, hardness (calcium).
Unless the water to be filtered is in a high hardness area, such as some parts of WA and North Queensland, a standard 4 stage unit is all that is required. A fourth stage 'post carbon' filter is required for all 'undersink Reverse Osmosis models. Any additional 5th stage cartridge should follow the post carbon filter for the addition of minerals and or alkalising. Unfortunately some sellers promote "more is better", which is not necessarily the case; most times, it is the seller who benefits with more replacement cartridges each year.
All water supplies have a measurement of TDS (Total Dissolved Solids) or minerals. These differ considerably.
We have all heard that Melbourne water is the best in the country. One of the reasons is that it has a low mineral content and no hardness - approx. 60ppm (parts per million). Adelaide with approx. 350ppm and Perth 400ppm. Sydney approx. 70ppm and Brisbane around 120ppm. Some parts of Northern Queensland are around 1200ppm because of the calcium and magnesium (hardness) present.
We do not recommend the total absence of minerals as with Distilled Water, as this is not recommended for drinking. However on the East Coast we would expect your pure water to contain 5 - 8 ppm after filtration, which is mainly trace minerals.
The other part of Reverse Osmosis is that the process itself makes the water slightly acidic around 6.4pH. Whilt stil lsafge to drink (WHO - World HEalth Organization), slightly acidic water is not recommended and, to improve the health benefits of reverse osmosis water, the addition of remineralising and remineralising/alkalising cartridges following filtration have become very popular to offset both the lack of minerals and to rebalance the pH level of the pure water produced.
The availability of both portable, countertop and undersink water filter units, allows all consumers to access pure water and take control of one of the most important human body requirements to keep us healthy.
Nominal rejection characteristics of the thin film composite (TFC) reverse osmosis membrane:
| Substance | % Rejection | Substance | % Rejection |
|---|---|---|---|
| Aluminium | 96 - 98 | Fluoride | 96 - 99 |
| Sodium | 92 - 98 | Bromide | 90 - 95 |
| Magnesium | 93-98 | Cyanide | 93-97 |
| Potassium | 92-96 | Sulfate | 96-99 |
| Calcium | 93-99 | Thiosulfate | 96-98 |
| Manganese | 96-98 | Silicate | 92-95 |
| Iron | 96-98 | Silica | 95-98 |
| Copper | 96-99 | Nitrate | 93-98 |
| Nickel | 96-99 | Polyphosphate | 96-98 |
| Cadmium | 93-97 | Orthophosphate | 96-98 |
| Silver | 93-96 | Chromate | 90-95 |
| Zinc | 97-99 | Bacteria | >99 |
| Mercury | 94-97 | Lead | 96-98 |
| Hardness | 93-97 | Arsenic | 90-98 |
| Radioactivity | 93-97 | Medications | 97-99 |
| Chloride | 92-98 | Chloroform | 90-95 |
| Ammonium | 85-90 | Tin (11) Sulfate | 83-87 |
| PCB's | 97-99 | PBA's | 96-98 |
The above percent of rejection is for reference only. Actual rejection will depend heavily on the exact chemistry, temperature, pressure and TDS content of the feed water.