Storage and transport of water under water
Placing water tanks or water pipes under water has the advantage that the walls are subjected to a much lower pressure difference. An underwater tank, where the walls are made from a flexible material like canvas, instead of metal or concrete, can adjust its volume to exactly the volume to be stored inside. Tennis tents are examples of such soft constructions on land. A pipe may economically assume a much larger diameter on the bottom of the sea, as compared to over land. That enables pipes with extremely low pressure drops and that the pipe also may be made of canvas. A common firehose is an example of such a pipe used on land – flat, transportable, cheap, and light when not used. Two examples for sweet water to drought-stricken Gotland are given. The first example is storing 1 million m³ from abundant-water- winters to summer, resulting in an annualised cost of 2 – 3 SEK/m³ ($0.2 – $0.3/m³). The other example is a 183 km long pipe in canvas transporting 2 m³/s sweet water to Gotland from mainland Sweden. That water is then roughly estimated to cost annually 1 SEK/m³ ($0.1/m³) used on Gotland. Could this be cheaper than desalination?