From Longman Dictionary of Contemporary Englishwater bottleˈwater ˌbottle noun [countable] 
DLOa bottle used for carrying water to drink
DLOa bottle used for carrying water to drinkExamples from the Corpus
water bottle• Out tumbled a water bottle and three children.• She'd come and give me a hot water bottle.• A hot water bottle in the small of your back should help.• She has a lid for the pan and a borrowed hot water bottle with her. 