Pump & Reservoir
The pump in a watercooling loop is responsible for pumping the coolant around the loop. The better the pump the better the flow rate and therefore the quicker coolant gets around.
Every water cooling loop as a reservoir which is responsible for simply holding and displaying coolant. What size, shape or colour really does not matter in a performance aspect - as long as it it can hold fluid and not leak then it is up to the job!
UK Gaming Computers not only use the best pumps and reservoirs out there but we also use "Combo" Pumps and reservoirs where both a are closely combined - For example the XSPC D5 Photon 170 Tube Reservoir with D5 Vario Pump has the pump attached to the bottom of the reservoir which minimises the amount of tubing which will not only improve performance as the coolant has less distance to travel before its cooled by the radiator, but also makes the loop look much neater.