Unlike Celebrity, there is no need to bring your own plastic water bottles onboard as Oceania has water bottles, free, when you are departing the ship for excursions, etc. Onboard, they provide each of you with a refillable water bottle and there are large bottles of still and/or sparkling water in your cabin that are refilled as ofter as you want. There are also water filling stations around the ship for those bottles. Some prefer to bring their own refillable water bottles onboard but Oceania provides you the water to refill those.