Must carry at least 3 litres of fluid, be big enough for all day rides and commuting to work.
Decathlon were doong a good price on a camelbac search the threads for it as someone put up a PSA
Decent Camel Back?
My last one just bust a zip at 6 years old. Been solid until now. Worth the price.
Amazon have the Evoc Freeride Trail 20L for £67 down from £125 if you don't mind having it in purple and already have a bladder.
even with shipping/tax this is a bargain!
http://www.jensonusa.com/Camelbak-The-Don-Hydration-Pack-2011
Might be a long shot but if you have any Lufthansa miles & more points
https://www.worldshop.eu/category/Backpacks/WorldShop_Sortiment_Sports_And_Wellness_Rucksaecke_?5
Got mine their last year.
Alternatively if you have a suitable backpack just get the Antidote Bladder and hose for £30 odd most places. My Halti pack which I use every day has a pouch in the back and an opening on top that you can use, much bigger pack than most Camelbacks so gives me an extra option if I need something a bit more "epic".