Jack,
I would advise him to take a look at all the factors that could affect hydration. When he experiences these episodes tell him to take a look back on the following and any other factors that could affect hydration. Such as weather, exercise levels, intake, type of intake, caffeine, prescriptions drugs, and diet as well as fiber. I may be wrong but common since tells us that intestinal and urine changes are usually caused by changes of habit or changes of our environment he may find that he is dealing with several factors that cause this outcome.
Let us know if he ever get to the bottom of this as it could be of help to others.
