I came across an interesting Microsoft research project, where they looked at what it took to manufacture and operate an underwater datacenter http://natick.research.microsoft.com/
According to the team, the idea behind these underwater datacentres is because 50% of the population lives near costal areas. Deploying servers along the coasts can help bring computing power closer to where the people are, reducing latency. Being submerged in water can also help with the heat exchange.
It is an interesting concept and there is more information in the short 2 minute video below.