From the Roman aqueducts to modern-day pipelines, bulk water transportation hasn’t changed over the years. Pipelines work well where there is an ongoing need over a long period of time so that the economic cost of construction can be recovered. However pipelines can be an expensive alternative where there the need is ad-hoc or in response to a particular short-term set of circumstances.
The alternative to piping water is to shift the volume by sea. This can be done in a number of ways including utilising converted oil tankers (VLCC or Suezmax) and flexible tanks inside 20′ containers (see Aquazeal).
Another method, which seems strange at first glance, involves towing water in an extremely large polythene bag behind a modified tug. In 1988 a Canadian engineer, Jim Cran, started developing what he termed a Medusa bag for this purpose.
These bags vary considerably in volume with the larger ones being able to hold many times the volume of a supertanker. They have already been used in perennially drought-stricken areas of the Mediterranean. In the late 1990′s, a company called Aquarius Water Transportation began towing water to the Greek Island in 500,000 gallon bags. Nordic Water Supply used bags 10 times the size to transport water from Turkey to Cyprus in the first half of 2001 but subsequently went broke. The use of polythene bags has been proposed in the US as well although environmentalists blocked the transport of water before it could get underway. So the use of this technology has been checked at best.
In his recent MSc thesis, Bruno Oreste Bellettini Cedeño of UNESCO-IHE Institute For Water Education, compared the cost of building an undersea pipeline from Brazil to Morocco to shipping water in large polythene bags from Turkey to Morocco. The interesting outcome from the comparison was the estimated cost to ship water in bags the 3,000 kms was US$0.41c/tonne. The often quoted cost of desalinated water is US$0.80c/tonne therefore the transport cost in bags is around half the cost of desalination, at significantly lower energy (therefore carbon cost) levels and without any of the environmental issues.
The cost of the equivalent 3,000 kms journey using a converted VLCC tanker at normal shipping rates is around US$4.40/tonne and at current shipping rates using a second-hand converted vessel is around US$2.75/tonne.
From an economic perspective, water importation using giant polythene bags does stack up against all other technologies. However most first world countries would not choose to rely on another country for something as important as fresh water. It is for this reason that most first world Governments have adopted a ‘desalination at any cost approach’ to water security. This may be an acceptable approach for a country like Australia, where there are no political points to be gained for saving money but running short of water, but where does it leave less well off countries that don’t have the billions needed to embrace desalination as the only solution.
A country such as Kenya, which is currently being ravaged by drought, is badly in need to additional fresh water to avoid a humanitarian crisis. The importation of water using the tug and bag method may well provide the short-term answer to the immediate situation.
The technology is certainly unglamorous compared to large scale desalination and waste-water recycling plants. It also doesn’t come with the intense lobbying by multi-nationals of politicians to spend the billions of dollars that is often associated with these types of big projects but this form or water transport is applicable in two circumstances:
- To supply water immediately to fulfill a specific need. This might be to stave off a looming humanitarian crisis, such as Kenya is facing, supplement existing water resource, or to cover a supply failure in a municipal water supply; or
- As a means to defer capital expenditure on desal projects until such time as the plant can be run at an economically efficient level.
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