Waterford, being one of the oldest cities in Ireland, is generally safe for solo female travelers. Like any other city, it has certain areas that are less safe than others but those are few. It's always recommended to stay aware of your surroundings especially during nights and in less crowded places. Dress modestly, don't flaunt expensive stuff, and always keep emergency contact numbers handy. Follow local customs and regulations. Locals are warm and helpful which makes it a pretty safe destination overall.