I personally would keep them separate or at the least setup controls within the space. Storing the water in sealed tubs maybe. I’ve got 3 separate safes for my firearms stuff, the main safe is water and fire rated and has humidity control, my bulk ammo safe also has humidity control. My 3rd safe is a small chest safe filled with ammo in rotation and magazines loaded up. I don’t need to store water but I do have 6 gallons in chest freezer as back up and to control the temp when power goes out. I’ve got a well with back up power systems and a river I could filter the water from if needed.