Ever run out of fresh water while boondocking?

Our 30 gallon fresh water tank is good for five full days with our family of six. We all understand how to conserve water. Having said that our water tank fill hose enters from the side so our actual capacity is less than 30. We have never ran out. Guages lie like politicians. I get the idea you are not filling your holding tanks? Or do you drain gray water onto the ground? Just cirious