[throwaway91111]

Reasearch indicates that fluorided water is better at covering the surface area of your teeth--brushing with toothpaste mostly removes the layer of plaque and allows the active ingredient to work better.

It's actually phenomenal how little dental research has ever reached consumer behavior or dental care.

[Arizhel]

Instead of fluoridated water, you can always just use fluoride mouthwash/rinse which many dentists now recommend to be used daily.

Personally I only drink RO water as tap water tastes bad to me, but I use a fluoride mouthwash (Crest) every night after brushing and flossing.