Hydration rucksacks on and off the bike?
You don't say how long your rides are or how much water is needed per hour.  Going by my personal experience, you'll want 1 bike bottle (also known as a bidon) per hour in neutral/comfortable temperatures, and more if it gets hot.  

I did a 12 hour ride and ended up sucking down 8-9 litres of water over the period (a bottle and a 2 litre pack, filled up three times) and that is consistent with a bottle an hour.

Locations: You can have two bottles inside the main frame triangle. a couple on the bars in holders, and two more aft of your seat.  You can also put stuff in panniers or on a bike rack on the back.

Bottles are available in up to ~800 mL sizes too - don't bother with the little ones.   Don't bother with insulated ones either - they plain don't work at keeping the water cool.  Instead you can add ice cubes to both bottles add the hydration bladder before topping it off with water.

Liquid - hydration bladders are terribly hard to clean and dry, but if you don't they will go mouldy.   Only put water in a water bladder, as per the instructions.  Anything with sugar should not be in the hydration bladder.

If you want to carry electrolyte drinks, use a normal water bottle for them.   I've tried them but they taint the plastic, so I can still faintly taste the electrolyte powder flavour several rides later.

I tried using the hydration pack on my MTB frame, but there was a long way to lift the water up the hose to drink it.  I found the pack to be good on the back, and because it was 2/3 ice helped keep me cool for the first few hours of my trip.