Yes, you can buy a water bottle along the Annapurna Base Camp trek route. The price of water bottles in the Himalayas are way more expensive than in the city. One bottle may cost you USD 2 and above.  There are water filling stations everywhere along the way. You can refill the water whenever it gets empty and save unwanted expenses. The water may be hard for you even if it is drinkable, so we recommend you use any purification method before drinking.