How much water carrying capacity do people plan on for a Summer Rasa?

Question from the unconsciously incompetent preparing for RASA: I am planning on doing RASA on my Salsa Cutthroat- This a gravel bike with very relaxed geometry which makes it extremely comfortable to ride for long periods- Far more so than any full sus MTB Ive ever ridden.Basically its the bike I LOVE for long distance off road adventures. I am pretty comfortable riding it on some of the chunkier terrain here in the Pacific North West.. Im aware that I will be "underbiked" for sections of the ride, but figure that there will be large sections Ill be perfectly biked for and so in the world of compromises, this seems to be a reasonable trade off in my mind. The other major advantage in my mind is that its lighter with less stuff to go wrong than a full sus bike. I had originally planned to put all me gear on the bike, but following RASA this year has made me re evaluate that plan and so Ill be using a back pack of some sort to aid with the hike a bike sections. Obviously a rigid bike is an unconventional choice, and whilst RASA has been done on rigid bikes, am I completely out to lunch here? Id value any insights from the consciously competent:)