How long will your water last in a campervan?
For two people with a 100 litre26.4 gallon fresh water tank, about 3.3 days, if each of you showers every other day and you wash up by hand once a day. Put in your own tanks and habits below to see when you need to fill up, and when the grey tank and the toilet cassette need emptying.
Your result
Empty the toilet first, after 2.5 days.
- Fresh water
- 3.3 days, using 30 L7.9 gal a day
- Grey water
- full in 4.5 days, 20 L5.3 gal a day
- Toilet
- full in 2.5 days
Thetford's guidance is to empty a cassette every 4 to 5 days with its Blue chemicals even when it is not full, so this never plans for longer than 5 days.
Measure your own starting values
LitresGallons per shower: run the shower into a bucket for 30 seconds and double it to get litresgallons a minute, then multiply by the minutes the water is running. The same works for the kitchen tap.
How it works
Days = tank size ÷ litresgallons a day. The fresh tank supplies drinking and cooking, showers, washing up, hands and teeth, and the toilet's flush water when the toilet takes it from the same tank. The grey tank collects the showers, the washing up, and hands and teeth. The cassette fills with water and urine at every flush. The starting 0.3 litres0.08 gallons of urine a flush, 5 times a day, is 1.5 litres0.4 gallons per person a day, inside MedlinePlus's normal range of 0.8 to 2 litresabout 0.2 to 0.5 gallons. If you mostly use other toilets, put in fewer flushes.
The 3 litres0.8 gallons for drinking and cooking start from EFSA's adequate intake of 2.0 litres (women) and 2.5 litres (men), about 0.53 and 0.66 gallons, of water a day from all food and drink, plus water for cooking and hot drinks.
When a tank runs low
In the Fontavio app you can filter the map to fill-up taps and to grey and black water dump points. You can see what's closest or pick a place on the map, then follow the compass or use navigation. With Pro, the route planner lets you pick the water stops along the way and open them in Google Maps as one trip.
Frequently asked questions
How long does a 100 litre water tank last in a campervan?
For two people, about 3.3 days with this page's starting values: 3 litres each a day for drinking and cooking, a 10 litre shower every other day, washing up by hand once a day, and the toilet flushing from the same tank. Showers make the biggest difference: with a shower each every day it is about 2.5 days. On your own, about 6.6 days.
For two people, about 3.3 days with this page's starting values: 0.8 gallons each a day for drinking and cooking, a 2.6 gallon shower every other day, washing up by hand once a day, and the toilet flushing from the same tank. Showers make the biggest difference: with a shower each every day it is about 2.5 days. On your own, about 6.6 days.
How much water does a campervan use per day?
With the starting values on this page, 30 L a day for two people, of which 20 L ends up in the grey tank. Your own figure depends mostly on showers, so it is worth measuring yours once.
With the starting values on this page, 7.9 gal a day for two people, of which 5.3 gal ends up in the grey tank. Your own figure depends mostly on showers, so it is worth measuring yours once.
How often do you empty a cassette toilet?
When it is full or starts to smell. Thetford's guidance is every 4 to 5 days with its Blue toilet chemicals and every 3 to 4 days with Green, even if the cassette is not full. A 17.5 litre cassette shared by two people fills in about 2.5 days by this page's figures.
When it is full or starts to smell. Thetford's guidance is every 4 to 5 days with its Blue toilet chemicals and every 3 to 4 days with Green, even if the cassette is not full. A 4.6 gallon cassette shared by two people fills in about 2.5 days by this page's figures.
Where can you empty a cassette toilet?
At a chemical toilet disposal point, which motorhome service areas and dump stations have. Fontavio maps them as black water and cassette dump points, and the dump stations near me page shows the closest ones.
Sources
- EFSA, Scientific Opinion on Dietary Reference Values for water (2010) (opens in a new tab) (checked 2026-10-20)
- MedlinePlus, Urine 24-hour volume (opens in a new tab) (checked 2026-10-20)
- Thetford, C260 series: service and support (when to empty the cassette) (opens in a new tab) (checked 2026-10-20)
- Thetford C263-CS cassette toilet, 17.5 L waste-holding tank (retailer specification) (opens in a new tab) (checked 2026-10-20)
- Thetford C200 cassette toilet with flush tank, about 5 flushes per 2 litres (retailer specification) (opens in a new tab) (checked 2026-10-20)
Get it before the next long walk.
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