I would love a closer up picture of how you actually rigged this, great idea! Thanks
Very easy to do.
I generally use single use bottles, but those that are a bit stronger than the normal ones.
To attach the bottles to the pack I just use bottle holders from Amazon.
I carry one spare. (they are not that robust)
Picture is example only.
To stop the bottle moving around, I just use an elastic tie around the base.
Usually elasticated shoe laces. (I carry a spare)
The blue cord on the RH bottle in pic below. (it stays on the pack strap).
The drinking tube can also be found on Amazon.
They often come with different size screw tops.
Make sure you get the right size!
Mine fits all standard single use bottles found in Spain.
This allows me to replace a bottle or change the bottle size if required.
I have a preferred bite valve that I replace if the one on the tube is not good.
(Yes I carry a spare bite valve as they can leak)
I could, to save weight, shorten the tube.
But I leave it long. It passes from one side to the other around the back of my neck through the load lifter straps. It all stays in place nicely.
Keeping the tube long gives me the option of using a bottle in my pack if required.
Though I have never needed to do this yet.
I carry 2-3 denture cleaning tabs, and clean the tube every couple of weeks.
Though I rinse it, and the bite valve every night.
Picture is example only.
This is it put together. All fits well.
Nothing moves around. All stays on the pack as set up.
As I finish my left bottle I can just unclip the bottles and swap them over without even stopping.
Though more recently, on long hot stages, I sometimes fill the right bottle with Aquarius.
Easy to just unclip to drink from it whilst walking.
It's a very flexible system.
One of the benefits, like using a bladder, is that it's easy to sip on the go.
Unlike a bladder, I can monitor consumption and remaining water levels.
For example, I know my 'normal' consumption is 10 kms / litre.
So I can easily glance down and drink more if required.
Or slow up consumption if I'm starting to run low.
Though I aim to never run out.
It's only anecdotal, but those I have walked with over the years, who rely on bottles in the their packs and hard to reach side pockets, seem to be more prone to issues that seem to be exacerbated by even mild dehydration. Joint pains, shin splints, blisters..... We don't get those issues. It's important to stay 'well' hydrated, and a 'sip as you go' system helps a great deal I think.
Of course, all is a lot easier on routes with regular villages, cafes, water fonts. But on my first Camino I also ran out of water (using a bladder) on the CF. Very unpleasant on a hot day.