i started off with a 2-gallon square collapsible water carrier (from campmor?)
stowed in the bob trailer for travel around new zealand. found it cumbersome
to deal with. also had the "what if" .....your one container leaks...

gave it away before the flight to australia. there i used 10 cheap and easily
replaceable 2L soda bottles. so 20 liters, plus a couple large bottles in cages
for up to 250 miles with no water in 105 degree fahrenheit.

you can get cheap ($5) 2L bladder bags on ebay. might be able to fit a couple
of those in a frame bag on each bike if no room in panniers.