I googled "BEST HYDRATION BACKPACK" about 6 years ago, this was the result. Perfect size for biking or traipsing thru the woods on a day trip with or without the hydration bladder, it holds 3l water and 10l of 'stuff'. Bladder was used like twice, and cleaned, dried and sterilized each time with stuff made for this purpose.
$35
https://www.outdoorgearlab.com/reviews/camping-and-hiking/hydration-pack/osprey-syncro-10
I also hae an osprey Atmos 65 AG available, see listing