Bottled water is about as safe as tap water. Both test positive for contaminants at about the same rate. Other considerations such as additives and hardness vary greatly by brand and municipality. Compare brands by researching water providers and ask a doctor about what is best for your health.
Additives such as fluoride and minerals such as magnesium can be found in certain sources of tap water and bottled water. Age, health history and other factors determine if these chemicals are harmful or helpful. Statistics about the contamination of the entire water supply are less useful than those about a local water supply. Both water agencies and private bottlers have contamination reports available for comparing the safety of local water to a bottled brand.