In fact, studies from the past decades show that coffee has significant effects our urinary sodium and potassium excretion [1], as well as hemodynamic and humoral effects [2]. 

A recent study from 2016 shows that low to moderate coffee consumption does not negatively impact our kidneys' filtration rate and thus does not deyhdrate our body [4]. Furthermore, caffeine in relation to physical activity decreases urine excretion [5]. Coffe is also thought to be similarly hydrating as water [6]. According to Maughan et al. three conclusion can be drawn from previous studies which investigated caffeine and the desire to void one's bladder [7]. Firstly, an increased consumption is associated with an acute diuretic effect [7]. Secondly, small doses of caffeine have little to no diuretic effect [7]. And thirdly, when consuming coffee regularly we get accustomed to the effects of caffeine and thus its effects are reduced [1].