Pass water
Definition 1 of 1
Pro Tip 1/3Medical Context
Often used in medical or healthcare settings when discussing bodily functions in a polite manner. 
The doctor may ask if you've been able to pass water regularly.
Pro Tip 2/3Not Explicit
'Pass water' is a less explicit way to say 'urinate,' and can be considered more polite. 
Excuse me, I need to pass water. Where's the restroom?
Pro Tip 3/3Euphemism
The phrase is a euphemism, meaning it's a milder way to express something that may be uncomfortable. 
Due to her bladder condition, she frequently needs to pass water.