Regardez votre sang-froid
Why did the comments start being about Arizona? The data centres in question are in Belgium and Dublin - hardly desert conditions. The problem with any scheme that tries to sell the heat generated as a resource (in effect using the external buildings of your customers as part of your heat sink) is that the majority of your problems will arise in the summer months, when your customers may be unwilling to accept this excess heat. If your data centre is generating enough waste energy to warm several buildings in the teeth of a Dublin winter, then there is something seriously amiss inside the data centre.
As for water-cooled air, Google's Belgian data centre does use river water cooling. The difficulty here is keeping any such system clean. Most Western capitals do, indeed, have major rivers running through them, but they're badly polluted major rivers, in many cases, whose water quality is outside of the control of any one body wishing to utilise it, unless (as is the case with Google's Belgian data centre) you include a full water treatment plant on site, to treat the water before using it. This is cheaper than using mains water, but does represent an extra cost and energy overhead, in what is supposed to be an energy-saving measure. Even when the risk to human health can be eliminated (where you are simply cooling machinery, and have less to worry about, with regards Legionnaire's disease, or what have you), the tendency for algae, bacteria and even fungi to build up in these systems and eventually clog them can mean you incur not-inconsiderable costs, down the line: once established, a population can become difficult to eradicate.
Finally - Register writers, please - interesting as they are, I have real problems reading these stories past the point where I encounter the words "Mountain View Chocolate Factory". Please, enough with retelling this not-very-funny joke, over and over again. I sometimes feel I'm being hit with a hammer by a bloke who demands that I laugh. We get it, okay?