Water!?

Does anyone struggle with getting their 12-24 month old to drink plain water? My 15 month old will drink LOADS of favoured water but it's a struggle to get her to have plain. Her grandparents introduced her to the flavoured stuff and obviously she's now resistant to boring old normal water. I've tried watering it down gradually but she just spits it out and refuses to drink anything (she's very strong willed already) I'm just worried all of the flavourings aren't good for her!