The minimum amount to urinate or defecate and be able to say asher yatzar is any quantity (kolshehu).
If you did not say asher yatzar immediately after finishing, you may still say the blessing until the next time you feel the need to urinate or defecate.
Say asher yatzar, even when you cannot wash your hands, such as when you do not have any water with you.
Note: In any case, your hands must be clean; if they are not, you must wipe them off on something before saying the blessing.
You may say asher yatzar for someone else if you need to say it also.
If you are eating and stopped to use the toilet, you may say either asher yatzar or the afterblessing on the food first.
After urinating while scuba diving, say asher yatzar. The water is sufficient as a head covering or, better, you may cover your head with your wetsuit sleeve.
Copyright 2015 Richard B. Aiken. Halacha L’Maaseh appears courtesy of www.practicalhalacha.com Visit their web site for more information.
This material is provided for informational purposes only – not a substitute for the consultation of a competent rabbi.