Most resorts provide drinking water at meals, but sell water $4-$5 for a 1.5 litre bottle at other times. Water supplies are generally from rain off corrugated roofs, springs or imported from the mainland.
English backpackers will be happy to hear that beer Fiji Bitter or Fiji Gold F$5-6 per can is in plentiful supply, and most resorts will also provide other forms of alcohol including cocktails $F10-18 depending on resort and cocktail. Buy supplies like alcohol or cookies in mainland if you are short on budget.
