Hello and welcome to the forum. Distilled water isn't good for them because it lacks trace minerals and elements that fish need. Regular tap water is fine as long as it's dechlorinated. Some good brand of dechlorinator are Prime and Aquasafe. There are other brands out there to choose from, though. Most people feed their bettas 2-3 pellets twice a day and, as Jynx said, fast their fish one day a week. They can also eat freeze dried or frozen daphnia, bloodworms and brine shrimp. Freeze dried should be rehydrated to avoid digestive problems.