RV Fresh Water Calculator

This calculator builds up a daily water budget from showers, drinking, toilet flushes, cooking, and dishwashing, then divides Tank Capacity by that total to estimate how many Days of Water you have. Tank Capacity has the largest effect on Days of Water: it's a pure linear numerator factor (its full elasticity carries through undiluted), while Number of People only reaches Days of Water indirectly, through its effect on daily usage, giving it a real but smaller elasticity. Number of People, in turn, has the largest effect on Daily Usage itself, ahead of Showers Per Day -- each additional person adds a full slate of showers, drinking, and toilet use, while an extra shower only adds its own fixed water draw. Flip the ratio and look at Gallons Per Person/Day instead of the daily total, and Showers Per Day takes the lead over Number of People: more people also spreads the day's fixed cooking and dishwashing water across more heads, which pulls the per-person figure down even as the total rises.

Cooking Water and Dishwashing Water genuinely add to Daily Usage, but their contribution is small enough at the default amounts that Days of Water and Refill Every can hold steady after a modest change to either one -- the effect is real, just easy to miss without changing them by a larger amount. Tank Capacity has no effect on Daily Usage or Gallons Per Person/Day at all, since those measure consumption, not supply. This is a planning estimate -- real usage varies with shower length, dish habits, and whether you're conserving water while boondocking.