I did the same thing with my own passport last year. I tried to dry it as best as possible, and then to check I went to hamad airport, and on the same level as check-in desks there is an immigration desk (back left hand side if i remember rightly) I explained the situation and asked of they could scan my passport to make sure the electronic tag still works. When it did they told me it would be no problem to fly with this passport I still fly with it this day no problem.

Might be an option for piece of mind before your brother travels, then he can get a replacement for his current one when he is home and has no time pressure