Water is free on the ship however not plastic bottles
They provide you with a personal metal bottle to carry ashore
They have Vero in the cabin
https://www.oceaniacruises.com/media/2019/OCEANIA+CRUISES+TO+ELIMINATE+PLASTIC+WATER+BOTTLES+IN+PIONEERING+GREEN+INITIATIVE+-+Partnership+With+Vero+Water+Will+Save+More+Than+Three+Million+Plastic+Bottles+Per+Year/