Reverse Osmosis 

Developed more than 40 years ago, Reverse Osmosis water filtration first arose for the purpose of desalinating seawater. Soon after, the process' decontaminating capabilities were recognized, reverse osmosis systems began to be offered for home water purification purposes. Seen as a viable option to the more costly and energy-wasteful distillation units, these systems were installed in homes as early as the 1970s.

The Reverse Osmosis process is based upon a semi-permeable membrane through which pressurized water is forced. It is based on the opposite process of Osmosis, which is the tendency of water to migrate from a weaker saline solution to a stronger saline solution. In Reverse Osmosis, water is forced to move from a stronger saline solution to a weaker solution through a semi-permeable membrane. Because slat molecules are physically larger than water molecules, the membrane blocks the passage of salt particles, resulting in desalinated water on one side of the membrane and a highly concentrated saline solution of water on the opposite side. In removing these particles, this process will also remove a select size of drinking water contaminants.

Reverse osmosis is a suitable water purification process when mineral-free water is the desired end product. Because the majority of mineral constituents of water are physically larger than water molecules, they are trapped by the semi-permeable membrane and removed from drinking water when filtered through a reverse osmosis system. This process will remove salt, lead, manganese, iron, and calcium, as well as some chemical components of drinking water, including fluoride.

Problems with Reverse Osmosis

Reverse Osmosis removes some contaminants from drinking water, it is not ideally suited for filtering municipally treated water. It does not remove such contaminants as chlorine and volatile organic chemicals (VOCs), because these contaminants are physically smaller in size than water. Thus Reverse Osmosis cannot prohibit them from passing through the semi-permeable membrane with the water.

By removing alkaline mineral elements of water, Reverse osmosis produces acidic water, which can be dangerous to the human body. In order to neutralize its acidity, it strips calcium and other essential minerals from bones and teeth. Trace elements of minerals in drinking water are important for human health.

Lastly, although Reverse Osmosis not as wasteful as distillation, is an inefficient process. On average, the reverse osmosis process wastes three gallons of water for every one gallon of purified water it produces. Furthermore, the high saline solution that is produced during the Reverse Osmosis process must be discarded, typically into the municipal wastewater system. High saline content in water can lead to high blood pressure and other health implications.