The most used root canal irrigant is the sodium hypochloride due to its antiseptic qualities. There are different NaOCl solutions - 2%, 5,25%, 7% or even 11%.

subtract irrigant from output to determine urine volume

By being rude and irrigant. God made us all different and we should respect that. So this shouldn't be a real question because no one should become racist.

When performing a Trial-of-Void a.k.a. a Trial Without a Catheter, a Urologist might fill the bladder with a set amount of sterile irrigant prior to removing the catheter. This will expedite the trial-of-void but may skew the results.

yes, they are interchangeable in the OR

I beg to differ - While I'm sure they are used interchangeably, they're not the same thing and shouldn't be substituted. Sterile water for Irrigation is not Isotonic (or iso-osmotic) and can cause severe hemolysis if used inappropriately. Problems arise when large volumes are used and when incompatible drugs are added to the wrong irrigant.