Water cooling reservoir is convenience part which eases process of air bubbles removal from cooling liquid at initial setup and eases monitoring of cooling liquid 's level and coolant's visual quality.

Note, that reservoir must always be positioned above water pump's inlet level for proper pump function.

The common confusion is about reservoir is that they have some effect on cooling performance – they are not!

The sole purpose of reservoir is uninterrupted liquid supply for the pump and… for uber looks.