Ocean water can and will be used to replace diminishing terrestrial sources of fresh water. With more than 97 percent of all water being seawater and mostly unusable, mankind— all six billion of us—gets less than 1 percent for all its needs. An increasing number of agricultural, industrial, and personal water demands are vying for fresh water—a finite resource. Today, about half the world's population has no reliable water resources and the number of have-nots is growing. This is particularly evident in areas where more than 50 percent of the world's population lives within 100 miles of a coastline. This situation has already created political unrest and conflicts.
Conservation, wastewater recycling, and desalinization technologies have helped extend existing supplies, but the scale of these applications is not enough to solve future problems. Each of these reclamation schemes has been around for a long time, however, implementation has been limited to a few places in the world
Wastewater recycling uses partially treated sewage effluent for non-human uses such as watering of landscaping and golf courses. Although being done today, pouring sewage on land is slow in gaining public acceptance. While this "gray water" is not safe for human consumption, it is perfectly safe for uses on land and some industrial processes.
Seawater desalinization works but it is very expensive and energy intensive. The concept is simple; boil the water and capture its steam, then condense it to get fresh water. But it takes a lot of thermal energy to break down the saltwater molecule. In parts of the world where energy is cheap, this is not a problem. For example, Middle Eastern oil-producing facilities flare off (burn) natural gas that is a by-product of crude oil production. Some flares have been burning for many years and are so massive that astronauts have seen them from space. This relatively cheap energy could be used for desalinization. But the rest of the world will have to buy hydrocarbons, mostly oil or natural gas, to run their desalinization plants. This makes the unit cost of distilled seawater very high.
Reverse osmosis has become the most widely used process with several hundred such plants operating throughout the world. Saltwater is pumped through a membrane, which traps the salts but lets fresh water through. While not as costly as boiling seawater, it is expensive compared to natural supplies of clean water. As costs of terrestrial water continue to rise, the process—the only practical desalinization means available at present—becomes more attractive. Ongoing research and development (R&D) has improved plant efficiencies and lowered costs. Plant sizes range from small units on ships and boats to large public utility installations for towns and cities.
Terrestrial agriculture within 100 miles of a coast is extremely sensitive to the price of water. The farmer cannot compete with low-cost imported commodities. Of course this is a transient situation, because farmers in other nations are not immune to the difficulties of finding water resources at the right price and quantities. For farmers forced out of business in coastal areas, their lands will be lost forever from food production, as developers snap up their property.
There is another solution to finding affordable water supplies in coastal zones: the development of salt-tolerant plants. Research in this area has been under way for the past three decades, with tomatoes and barley being successfully grown in brackish water (low salinity seawater). But to use pure ocean water (which contains 3.5 percent salts) will require additional research. The remarkable work in the past few years for genetic modification of plants may be the key to solving the problem.
Full desalinization implementation will require further R&D and considerable public and political action. Infrastructure requirements range from minimal investment—with facilities that produce fresh water simply being linked to existing public utility water systems—to extensive with gray water reuse requiring a system of new pipelines. Direct use of ocean water in salt-tolerant agriculture will also require dedicated pipelines as the water cannot be commingled with fresh water and seawater is naturally corrosive.
Using seawater for agriculture is not a matter of curiosity, it will be a necessity. Scientific research and technological R&D need to be accelerated. Together with desalinization projects and recycling of gray water, the use of ocean water can help steer mankind away from future global water shortages.