How this works: figures below are typical RV usage benchmarks, not your exact numbers — actual usage varies a lot by habits and shower head/tap flow rates. Use this to plan with a sensible buffer, not as an exact countdown.
Your tanks & crew
Grey water is sink/shower waste water. Most RVs handle toilet waste separately in a cassette or black tank — that's tracked separately below since it fills from flushes, not general water use.
Daily usage per person
Defaults are typical motorhome/caravan figures per person per day. Adjust any of them if you know your own habits run higher or lower.
Drinking & cookingLitres/person/day
Washing & dishesLitres/person/day
ShowerLitres per shower
Toilet (cassette/black tank)
Optional — only fill this in if you want to estimate cassette/black tank duration too. Factors in flush water AND actual waste volume, not just flushes — that's what really fills the tank.
Waste volume defaults to a typical adult average (~1.4L urine + ~0.2L solids per person per day) on top of your flush water — this is what actually fills a cassette faster than flush water alone suggests.
—
days before you need to refill or empty
—
—
Fresh water lasts
—
Grey tank fills in
—
Cassette/black tank fills in
Ways to extend it
Small habit changes that add real days to your water supply when free camping.
Use a spray nozzle or navy-shower technique — wet, taps off to soap up, quick rinse. Can cut shower usage by more than half.
Wash dishes once a day in a basin rather than running the tap continuously.
Use campground showers/toilets when available to preserve your own tanks for when you're off-grid.
Carry a couple of extra 10–20L water containers as a buffer for longer free-camp stretches.
Fix any dripping taps before a trip — a slow drip adds up over days.
Share your water plan
Handy to keep as a reference for the trip, or send to a travel companion so you're both working from the same numbers.