Hawaii is free from malaria, yellow fever and most other diseases endemic in other tropical countries. Mosquitoes are present throughout Hawaii but are rarely an annoyance on the dry coastal areas. Water is safe to drink except from mountain springs where purification is needed. The only real threat is the Sun - sunstroke, prickly heat and other skin irritations particularly in the more humid months from August to November when light, airy clothes are essential. Take plenty of sunscreen and a good brim hat with full UV protected swimsuits recommended for small children.
Doctors, dentists and pharmacies are found everywhere but are extremely expensive as are hospital beds and emergency operations.
If swimming, it is advisable to stick to the public beaches which have lifeguards. Hawaiian beaches often have dangerous rip tides and currents around its passages and the state uses official flags to represent swimming conditions.