Is flavoured water good for you?

It depends, it may contain sweeteners or sugar.

Depending on how it's flavored it may not be bad for you. Like you, I find plain water boring (unless I'm REALLY thirsty) so I drink sugar-free beverages (e.g., Crystal Light, Mio, etc). Different companies that make flavored waters use different additives, but basically if that's what it takes for you to get in more fluid a day, then it's fine (it beats drinking nothing at all). Try to opt for ones with the least amount of artificial ingredients/colors if you're wanting to keep it as healthy as possible OR make your own flavor-infused water by adding various fruits or veggies to a pitcher of water, put in the fridge, and letting it sit for several hours or overnight. 

No it has sweeteners.

We use a brand named Hint

The water's good.  The flavouring is probably not good.  The sweetener is definitely not good.  Try boiling your water and flavouring it with tea.