The term "water transportation" refers to the act of moving substantial volumes of water from one location to another. There are three main categories into which most water transportation activity can be divided: aqueducts, shipments via containers and towing across large bodies of water. These various methods can be used to move water from a location where it is abundant to an area where it is needed. Water transportation can be used for irrigation of otherwise arid lands, the delivery of fresh drinking water to large municipal areas and many other purposes.
In modern engineering terms, "aqueduct" can refer to closed-pipe systems, open canals and other similar methods that are commonly used to transport water. Aqueducts have been used for transportation since the seventh century BCE, when they typically consisted of large, raised constructions that were capable of diverting substantial volumes of water to population centers. Open canals and raised aqueducts are still in use, though most municipal water transportation systems use closed pipes. These pipes tend to create more friction than open canals, and in many cases, pumping stations are used to keep the water moving if the downward incline of the system is not sufficient.
Water is also commonly transported in containers, using both trucks and ships. Up until the late 1800s, liquids such as water were transported only in casks, though various technological developments led to the creation of container ships. One issue that can affect water transportation using tanker ships is known as the free surface effect. This effect describes the likelihood of a large surface area of liquid in the hold of a ship adversely affecting the stability of the vessel, which is typically dealt with by creating segmented or partitioned areas within the hold. Tanker trucks can also be difficult to drive for this same reason, and they often contain a system of baffles as well.
Another method of water transportation is towing. One way to accomplish this is to use a tugboat to tow an iceberg, because the ice is made up of fresh water. Fresh water also can be towed through saltwater in a liquid state if it is placed in an airtight bag. The fresh water is less dense than the saltwater, so the bag will tend to float at the surface. Designs for large bags capable of transporting water in this way were first tested in 1990.
