There is no safe tap water so be prepared with bottled water, which is usually easily obtainable. The only other option is ranon'apango RAN-oo-na-PANG-oo or rice water water used to cook rice, which will therefore have been boiled. It's particularly important to plan ahead if visiting rural areas. It is worth taking with you some chlorine tablets, which can be used to make the local water drinkable.
In towns, roadside drink stands, stores and bars are plentiful. Most sell a range of drinks including bottled water, Fanta, Coca Cola and Madagascar's beer, Three Horses Beer "THB". You can also try the bubblegum flavored soda 'Bonbon Anglais' similar to South American Inka Cola, if you are very brave!. Be warned that this may be sold as 'limonade' - leading you to think it may be lemonade.
Home brewed rum, and creme de coco, is also available - in many flavours!