hold one's water

verb2

1. •
   (old-fashioned) To restrain one's urge to urinate.

   • […] and if there is much oozing of blood, the application of ice to the penis. The patient is then instructed to hold his water as long as possible. — 1877
2. •
   To be patient; to control one's impulses.

   • Hold your water, I'll get to you in a minute.