Sea Water as a Source of Drinking Water
With 75% of the earth covered in sea water, finding a safe, economical way to convert sea
water into drinking water, or potable water, would help alleviate the stress on existing fresh
water sources. Over the last century, improvements have been made in the technology required
to convert sea water into drinking water. However, more improvements need to be made to
make the technology cost-effective and available to wider segments of the earth’s population
where fresh water supplies are inadequate, but sea water is available.
Desalinating Sea Water
Converting sea water into drinking water requires a water treatment process that removes salts
and minerals from the sea water. The process of creating fresh water from sea water is called
desalination.
Desalination is not just one step; it is a series of steps similar to what water from other sources
(such as lakes or wells) must go through to produce clean drinking water. For example, the first
step in treating sea water lake or well water is to remove large debris, such as dirt or sand. The
next few steps remove progressively smaller particles, like microorganisms and minerals.
For fresh water, this progressive water treatment might involve running the water through a
series of filters and membranes.
For sea water, the principal method is to vacuum distill the water, which means boiling the water
at a lower pressure so that it takes less energy to boil the water. However, membrane
technology is improving in this area, and this provides a more energy efficient alternative to
vacuum distillation, because desalinating through membranes takes less energy than vacuum
distillation.
Challenges of Sea Water Desalination
Of course, desalinating sea water on a large scale requires more energy than cleaning water
from fresh water sources. It also requires specialized equipment that is more expensive to
manufacture and purchase. Therefore, converting sea water to fresh water is more expensive
than cleaning water from fresh water sources.
Another challenge of desalination is that when a desalination plant takes in water, it also takes
in small wildlife (for example, fish eggs and plankton) that are not strong enough to escape the
current created by the suctioning of the sea water. Currently, there are no cost-effective ways of
minimizing or eliminating this factor. In the United States, desalination plants cannot operate
next to oceans in a cost-effective manner because the Clean Water Act requires that
desalination plants reduce mortality of wildlife by 90%.
Desalination also requires disposal of the process’ by-product, which is mostly salt and other
minerals. Because most desalination plants are next to sources of sea water, the most efficient
manner of disposing of the by-products is to distribute them to the bottom of the ocean floor.
Unfortunately, the increased salt and mineral concentration introduced at the site where the byproduct is deposited kills the sea life in that surrounding area.
One method of minimizing this destruction is to include waste or by-product from other water
treatment processes (for example, sewage treatment) to dilute the concentrate. In the United
States, the additional waste or by-product has to meet federal regulations to be safely disposed
of in the ocean, so the desalination by-product is not being diluted by untreated or unregulated
waste.
Sea water is a promising source for drinking water, but water treatment technologies must
advance to economically meet the needs for new potable water sources around the globe.