During my last visit to Bali I was recommended this product that is available at any corner store, matahari supermarket, it is called "Larutan Penyegar - Kaki Tiga" and is found in the drink section at approx 50cents a 320 ml can.
Easily identified with a picture of a rhino on the can (Dontlet this deter you) comes in a variety of flavours orange, grape, lemon which are all quiet palatable.
Drink up to 3 cans a day and you will not fall prey to the nasty bali belly, you can drink more then 3 cans a day I think I drank about 5 cans a day as it is also recommended for: body heatness, flu, gingivitis, sore throat, consitpation, so as you can see it is a remedy for lots of ailments. And is also safe for children.
HIGHLY RECOMMENDED to others and they have thanked me for not allowing them to get sick during their holidays.