Osmosis, by definition is a “slow change in concentration”. This is when we take a solvent (like water) and squeeze it through a semi-permeable membrane, which leaves a more concentrated solution on one side of the membrane and a more diluted solution on the other side.
What? Ok, let’s move on to how the process is used:
In some uses of reverse osmosis, the more concentrated part is what we want. An example would be making maple syrup, where reverse osmosis separates the water from the sap, leaving the syrup.
In other cases, like desalinating seawater to create freshwater, the more concentrated part is what we want to get rid of (the salt), in order to use the water that makes it through the membrane.
You could add sugar to a glass of iced tea, mix it up until it dissolves, put the iced tea through the reverse osmosis process and actually remove all of the sugar back out of the tea.
The most common example of the RO process that most people see and hear about is the use of it in drinking water systems. In a high quality RO drinking water system, reverse osmosis is only one of five stages. The first stage is a sediment filter, which intercepts the larger particles present in the water. From there, the water travels through two carbon filters, which remove organics. The next stage is now the membrane, which is where the reverse osmosis actually occurs. At this point, most contaminants have been removed and the water is off to the fifth stage to be de-ionized, which “polishes” the water for taste and the elimination of odors.
The following list is an example of what the RO membrane removes from water. In most cases, 90 plus percent of these contaminants are intercepted prior to reaching your glass.
Sodium Sulfate Cyanide
Chlorine Nitrate Iron
Zinc Mercury Selenium
Phosphate Lead Arsenic
Magnesium Cadmium Barium