In 12 days, no matter what you do, someone is going to have to be there to water your rats. I am kind of assuming you have a bunch... but I know from experience that one glass bottle of water lasts my mice a day... we are speaking rats here. You don't have any friends that can do it for you? Maybe a local breeder in your area you can hire... or just someone you can hire to check on them every couple of days?