Our 100 gal lasts us about 2 weeks but we could likely stretch to 3 weeks, so you should be safe with about 4 days not allowing the tap to run when cleaning teeth washing hands etc at full belt and taking navy showers, which we do x 2 every other day and we wash dishes at least once per day sometimes twice just in mindset of conserving water.
We also carry filtered water in containers for drinking, coffee making, cooking using main tank for just washing and bathing. Also we carry a couple of 20 gal containers of water as a back up, which in all fairness we've rarely used in over 13 years - others might carry a few 5 gallon ones.
