Back in the day, before watercooling was very mainstream, OverclockersHideout sold radiator-less kits. In fact, a radiator wasn''t considered "standard" at that time. The first kit that came out with a radiator was BECooling's original Aquastealth with rubber hose (my first jump into watercooling

).
Anyhow back to my point, water temps will not just climb and climb and climb. They will increase and eventually plane off, depending on what your air temps are, etc. The way that OverclockersHideout did it was by having a large igloo cooler with a sumbersible pump in it. there would be an in line and an out line and go into the PC, hooking up to the H2O block. The thing to keep in is that at that time, CPUs were not putting out as much heat as they are now and that this solution is only mildy better than aircooling. To be effective, you'd have to bury a reservoir underground or just have a huge tank that you use. Something to consider would be a large reservoir (igloo cooler size) and a small radiator with a fan on 5V. I still don't feel that it is overall a good solution.
-Kevin