Hi there,
If I have understood your request correctly, you wish to build a water cooled machine for hosting web sites and the host it in a DC somewhere? If so, yes, all most all DC provide co-lo services (http://lmgtfy.com/?q=co-lo+uk). Where geographically would you like to host it, you would get better recommendations if you let us know?
I know people telling you what to do is annoying, but my two pence would be not to water cool a box and us it to host web sites; that is completely the wrong way of doing things IMO. Not just liquid cooling but also overclocking to host public services. Why are you choosing this method, just out of curiosity? I'm not criticising you but I think you have missed a trick here and perhaps haven't realised it.