While these websites do all of the work for you, the shipping costs can run very high because of the heavy weight of the water bottles. If you can't swing the high shipping costs or if you are a DIY kind of bride, you will be pleasantly surprised at how easy it is to customize water bottles for your wedding.
If you choose the DIY route, you are going to need water bottles with the labels removed and blank labels. I suggest ordering weatherproof labels from www.onlinelabels.com. They will withstand smudging when submerged in ice or water. Use Online Labels' Maestro Label Designer (trial always provided with a new order) to design your personalized labels. Then, simply print from your inkjet/laser printer and affix to the water bottles. Not sure how to design your label? Try using a monogram or the design from your invitations as a start. And don't forget to print test pages before the bulk print!