I don't know why people always think of The Water Is Wide - does anybody pay attention to the words?! It's about Broken Love!! It's like that Sting song that everybody assumes is about love, the one that says, "Oh, don't you see, you belong to me." If you listen to it, it quickly becomes clear that it is about borderline-pathelogical jealousy! Not that there isn't a really stupid attempt to make TWIW into a wedding song with lines like,When Love explodes and fills the sky...."
I'm a cantor. I actually had to sing that, and the mere memory of it serves to make my want to hurl. For anyone with an ounce of curiosity, go ahead and look at The Water Is Wide. It MUST be in the database, and plugging it into google.com works just fine as well.
If you want Gaelic wedding suggestions, go to google.com and plug scottish and wedding in. In my rambles 'round the net I must have come across half a dozen sites all about it. And if you choose to have Gaelic songs at your wedding, go ahead and find out what they mean, you don't want to make that Sting/TWIW mistake! If she comes from Uibhist, somebody in her family is probably a speaker, and be assured, NOTHING is more important to a Gael than poetry.
George is a great guy for suggestions. If anything floats through my head, I'll add it here as well.
Best Wishes to the Bride,
ciarili