I do not use a back system. If I go on a long ride (>50 miles) I will put an extra bottle in a rear pocket. This time of the year when it is still cool I can get away with that.

When it warms up and I need more water, I usually stop and ask someone who is watering their garden or lawn and refill.

I have used back systems for mtn biking but can not imagine using one on the road. I guess I like the weight on the bike instead of me.