When we went in August, I packed up a box of "stuff" - sunscreen, food, etc. and added in a water bottle filled with distilled water - and sent it down a week before via FedEx Ground. It was only a 16.9 oz bottle which wasn't quite enough for my CPAP for our 6 nite stay, but there was only one night where I needed to use "regular" water.
If you pack two 16.9 oz bottles in your checked baggage, you should be fine. Just pack it in a plastic bag and put both bottles in another larger plastic bag to prevent against spillage.
Also, you can carry your CPAP on as carry-on baggage and it does NOT count against your carry-on total. So if your airline lets you carry on a purse and one carry-on item, you can take your CPAP and still have a purse and a carry-on item. My sleep center said you should NEVER check your CPAP or just toss it up into the overhead bin.