It is recommended that you drink at least three liters of water a day or more. You should be drinking as much water as you can while you are here. It is an electrolyte powder which is similar to Gatorade and can be easily packed anywhere you go. 2-3 of those packets and a table spoon of salt in a large bottle of water is perfect to replace all the salts and electrolytes you sweat out every time you surf. It is a very good thing to have with you at all times.
Malaria is rampant throughout Indonesia and especially in the outer islands.
Bali is safe enough from Malaria, but the rest of Indo is not. The best way to avoid it is of course to not get bitten by mosquitoes, period. This means long sleeves and long pants at night, or a god mosquito repellent that has a high concentration of deet. If you wear short sleeves and short pants, use repellent. More information about Malaria can be found on the Health Tips page.