It seems almost farcical to question the merits of hydration for our renal health but is this actually the truism we have been lead to believe? Where does the recommendation of ‘8 glasses a day’ come from and what is the level of evidence to support it and in whom? Or should we in fact be setting our sights on output ie. 24 hr urinary volume, over input. Do all kidneys love water – or does this relationship change with the progressive impairment seen in CKD which affects up to 30% of our middle-aged population? When does hydration become harassment?