Great analogy for cloud computing.

Imagine if tap water didn’t exist. Every household would need to dig a well. Doing so would be a pain. Wells are expensive to build and expensive to maintain. You wouldn’t be able to get a large quantity of water quickly if you needed it—at least not without upgrading your pump. And if you no longer needed the well, there would be no store to return it to, and no way to recoup your capital investment. If you vacated the house, or the proper plumbing was installed in your house, you would have invested in a well you don’t need.

Tap water fixes all of that. Someone else spends the money and builds the right plumbing and infrastructure. They manage it and ensure that the water is clean and always available. You pay only for what you use. You can always get more if you want it.

That, in a nutshell, is what cloud computing is all about. It is data center resources delivered like tap water. It is always on, and you pay only for what you use.

 

Source:

Programming Windows Azure
Programming the Microsoft Cloud
By Sriram Krishnan