The compartment is approx. 39x23cm and has a hole at the bottom right (drain) in case the water bag leaks.
My older Camelback 3l measures 44x20cm empty and goes in. However, I have never filled it over 2l and it folds a bit. As a result, the last 1-2dl are sometimes difficult to get out.
The 2l from Source and Camelback should fit perfectly. Both systems have advantages and disadvantages:
Source:
+ Closure is not bulky in thickness. Especially important for this backpack.
+ Valve is hardly ever triggered by mistake
+ Valve and bag were still tight after 1 year of travel and almost daily use.
+ Lighter than Camelback
- Valve requires greater actuation force. (If you do not drink 5-8l through the valve over several days, this should not be a problem).
- Valve consists of several parts. Therefore more difficult to clean
+- made of stiffer material. Better inherent stability but also bulkier.
Camelback:
+ Valve easy to operate
+ Valve easy to clean
- Valve easy to operate. Drips with light pressure.
- Valve/closure is no longer leak-proof in my case.
- heavier than source
+- Soft material. More flexible but tends to collapse when it is not hooked into the top of the rucksack.