So, before we get into that, let's take a look at what a waterblock actually does and how it works. I suppose the first part is easy – a waterblock sucks heat from the CPU, right?
Well, sort of... not really. But yes... no.
Why the confusion? Well, this is a huge misconception. Let's rephrase this properly: A waterblock obtains temperature equilibrium with the heat spreader of the underlying chip. That's it. No sucking involved.
It's the same misconception as air cooling – a heatsink doesn't actually cool the chip. It simply provides a greater surface area for the heat to spread over. Since there's more metal to heat up, there's less heat in each molecule of metal – so it seems like it's cooling. The real definition of cooling is the removal of heat from the system – no heat is being removed here, just simply spread out. Instead, it's the fluid—be it air or water—that actually does the cooling.
This probably seems pedantic – the block cools, or the block spreads the heat and thus lowers temperature. It may seem the same, but it's not – it radically changes how we need to look at water blocks. We can distil everything above down to one basic statement:
A block's function is not to cool your CPU – it's to provide the most contact with water molecules as possible."