Reverse Osmosis: How Reversing Nature Led to
Even though most of the Earth's surface is covered with water, very little of it
is safe for drinking as is. Most of the world's water is contained in the oceans
as sea water. The high content of salt in sea water makes it unfit for human
consumption. Drinking sea water eventually leads to death. An attempt to make
sea water drinkable led to the development of a water filtration process known
as reverse osmosis.
Reverse osmosis is a water filtration method that was developed in the 1970s. It
was first used in desalination, the process of getting fresh water from sea
water. Reverse osmosis soon appeared in the home water filtration market as a
better working alternative to expensive and inefficient distillation systems.
The reverse osmosis process reverses a natural tendency of water in relation to
a semi-permeable membrane. A semi-permeable membrane lets through some atoms and
not others. If you have a area of water with a small amount of dissolved
material on one side of a semi-permeable membrane, and water filled with a
higher concentration of dissolved material on the other, water tends to move
through the membrane toward the more highly-concentrated solution until the
solution is equal on both sides. Reverse osmosis reverses this process so that
water moves toward the weaker solution, further diluting it.
When reverse osmosis was developed to desalinate sea water, it was found that
the semi-permeable membrane block other contaminants in addition to salt. After
this discovery, reverse osmosis water filter systems were developed.
Since most minerals contained in water have molecules larger than the water
molecules, reverse osmosis is very effective at removing mineral content from
water. Minerals like salt, lead, manganese, iron and calcium are successfully
filtered by reverse osmosis home water filter systems. Reverse osmosis is also
able to remove some chemical contaminants, including the fluoride that is
present in many municipal water systems.
Unfortunately, most municipal water systems also contain contaminants like
chlorine and organic chemicals that are physically smaller than water molecules.
Any contaminant that has molecules smaller than water molecules passes through
the semi-permeable membrane and stays in the filtered drinking water.
Reverse osmosis water filter systems can actually make water more dangerous in
some cases. If certain alkaline minerals are removed from water, then the water
becomes more acidic. In an attempt to lower the acidity of the water, your body
may take calcium and other minerals from your bones and teeth. Reverse osmosis
also removes trace amounts of minerals from your water, leaving it tasteless.
Reverse osmosis filter systems are also very inefficient, wasting about three
gallons of water for every gallon of purified water that it produces.
RO water filters can be very useful in rural areas where municipal water is
unavailable, but river or sea water is plentiful. Reverse osmosis is also a very
useful process in some of the world's desert areas that have almost no drinking
water, but usually have an abundance of sea water.
Reverse osmosis is also useful as a step or phase of water treatment used in
combination with other methods. Some home filtration systems use reverse osmosis
in combination with carbon filtration and UV light treatments.