Malaria is not a concern in southern Thailand, but there have been a few documented cases of Dengue Fever, so it is advisable to dress appropriately in the evenings and bring sufficient mosquito repellant along!
The sun can be very harsh as well, so make sure that you have an ample supply of high factor sun-screen. Water from the taps can be used for bathing and brushing your teeth. Drinking water is readily available, and in many places, is offered free of charge.
There is a fully equipped gym within 5 minutes walking distance from the Dive Centre if you're worrid that you are going to miss out on your training sessions!