The grey-water tank
It receives almost everything the fresh tank delivers and is often smaller: it is what ends many stays. In the example, 80 L of grey water last 2.5 days, barely longer than the 2.4 days of the 100 L fresh tank.
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How many days can your campervan or motorhome stay off-grid?
Four reserves decide how long you can stay without services: the fresh-water tank, the grey-water tank, the toilet cassette and the leisure battery. Enter your volumes and habits: the calculator gives each one's days, and the one that sends you back to a service point first.
Figures checked on
Work out your off-grid days
The calculator opens on an example: 2 people in July (Southern France, Italy, Croatia, northern Spain), 100 L of fresh water, 80 L of grey water, a 17 L cassette, 100 Ah of lithium and 200 W of panels. Replace them with your own figures: the result follows.
Your off-grid days in July
2.4 days
The fresh-water tank runs dry first: you will need to refill. 2 full days ahead.
- Fresh waterfirst2.4 days
100 L ÷ 41.4 L per day
- Grey water2.5 days
80 L ÷ 31.8 L per day
- Toilet cassette3.5 days
17 L ÷ 4.8 L per day
- Battery14 days
1,020 Wh usable ÷ 74 Wh deficit per day
On a knife edge: the panels cover 94% of the load. With 10% less sun, the battery would last ≈ 5.3 days.
What would gain you the most
- Showers: none on board+1.1 days
- An extra 20 L jerrycan of water+0.1 days
Where these figures come from
| Drinking and cooking | 4.8 L |
|---|---|
| Dishes | 3.6 L |
| Washing (no shower) | 5.4 L |
| Shower | 6.9 L |
| Total per person per day | 20.7 L |
In July, the Nomad score counts × 1.2 for water. Default electricity use: 1,500 Wh × 0.85 = 1,275 Wh; a figure you type is used as it is.
- Daily consumption
- 1,275 Wh
- Daily solar output
- 1,201 Wh
- Usable battery
- 1,020 Wh
Indicative estimate, with no refill or emptying during the stay. It does not replace reading your gauges.
How much water does a campervan use per day?
The calculator adds up uses instead of starting from an average: drinking and cooking, dishes, washing, showers. The ranges come from our van water guide; the calculator takes their middle, then applies the Nomad score's seasonal multiplier.
Beware of the 4 L per person per day figure: that is drinking and cooking only, never total use. Add dishes in a bowl and washing, and a frugal stay comes to about 11.5 L; with a quick shower every day, 23 L. In summer the score counts × 1.2.
A hot pressurised shower every day takes the sum to 36.5 L per person: more than the 18–30 L our guide gives for comfort use (and its 22–28 L for an equipped couple with a daily hot shower), because the calculator adds up the middle of each use. Treat this option as the pessimistic case.
Everything that comes out of the tap, except what is drunk and cooked, ends up in the grey tank: dishes, washing, showers taken on board. That is why the grey tank fills almost as fast as the fresh tank empties.
Tanks, filtration and water points are covered in our guide: Water Self-Sufficiency in a Van — The Complete 2026 Guide (Usage, Filtration, Maintenance)
| Use | Range | Used |
|---|---|---|
| Drinking and cookingper person per day | 3–5 L | 4 L |
| Dishes in a bowlper person per day | 2–4 L | 3 L |
| Dishes under a running tapper wash-up | 8–15 L | 13.8 L per person per day |
| Washing, no showerper person per day | 3–6 L | 4.5 L |
| Quick showerper shower | 8–15 L | 11.5 L |
| Hot pressurised showerper shower | 20–30 L | 25 L |
Under a running tap the same wash-up takes 8–15 L against 2–3 L in a bowl: the calculator scales the bowl figure by that ratio.
What changes the result most
Showers and dishes
The shower is the biggest water use. In the example, giving up showers on board takes the stay from 2.4 to 3.5 days (+1.1 days). Same logic for dishes: 2–3 L in a bowl, 8–15 L under a running tap for the same wash-up.
The season
It works both ways. In summer the score counts × 1.2 for water and × 0.85 on the default electricity use; in winter, × 0.8 for water but × 1.3 for electricity, and the panels make 4.3 times less in December than in June (Southern France, Italy, Croatia, northern Spain). Even in July the example's battery is on a knife edge: the panels cover 94% of the load, so with 10% less sun it goes from 14 to ≈ 5.3 days. In December it lasts only 0.6 days.
The battery
An AGM battery is used to 50% of its capacity (the depth of discharge Victron considers the most economic for that type of battery), against 85% for lithium in the Nomad engine: for the same amp-hours, lithium gives 1.7 times more usable energy. Without sun, charging while driving or on hook-up takes over: Charging without sun: alternator, shore, generator
Cutting use at the source moves the limit more surely than a bigger tank: dishes in a bowl, short showers, rinse water reused. Volumes, separating toilets and legal emptying are covered in our guide: Grey water and toilets: the van's outlet circuit
Where to empty and refill
When the calculator says stop, you need a service point: grey water and cassette in the facilities meant for them, never on the ground, in a ditch or down a storm drain. Networks and rules change from one country to the next:
- FranceAires de service: a service point to empty grey water and the cassette and to refill, often token-operated.
- SpainÁreas de autocaravanas: grey- and black-water dumps and drinking water, depending on each area's equipment.
- PortugalASA areas: emptying, drinking water and rubbish.
- ItalyAree di sosta attrezzate, with a “camper service” to empty and refill.
- GermanyStellplätze, sleeping in a car park and the low-emission sticker: the country's rules.
- CroatiaWild camping, fines, campsites and aires: the country's rules.
- MoroccoCampsites and guarded areas: water, emptying, sometimes electricity, and a warden.
Method and limits
Water: the uses in the table above × the number of people × the Nomad score's seasonal multiplier (× 1.2 in summer, × 0.8 in winter, × 1 in spring and autumn). Grey water receives everything except drinking and cooking, showers taken on board.
Cassette: the calculator counts ≈ 2.4 L per person per day (urine, flush water, solids and additive), of which ≈ 1.3 L is urine: assumptions taken from our guide, not datasheet figures. Thetford gives 17 L for the waste tank of its C200 cassette and 19.3 L for that of its C400 series: at this rate, 3.5 to 4 days for two. Separating toilets are not counted as a limit: their urine bottle needs emptying more often, but more easily.
Electricity: the Nomad digital twin's engine. Output = panel watts × the region's peak sun hours (from 2.5 h in Lapland to 6.5 h in Morocco) × 0.7 for losses × the month's sunshine relative to an average month (1 = the year's average); a run of overcast days keeps only 45% of it. Usable battery: 85% for lithium, 50% for AGM, at 12 V. Default use: the score's van reference (1,500 Wh/day) × 0.85 in summer, × 1.3 in winter; a figure you type is taken as it is, as the chosen month's use.
The calculation stops at 30 days and assumes no refill or emptying on the way. It describes an average day, not a weather forecast or a PVGIS simulation: a heatwave, guests or a grey week shorten the stay. Keep a margin of at least 20%, as our water guide advises.
Why the first reserve to run out decides everything — the full method is in Van Self-Sufficiency: Power, Water, Food — the Complete Route-by-Route Breakdown
Frequently asked questions
How many days can you stay off-grid in a motorhome?
As long as the first reserve to run out allows. In our example (2 people in July, 100 L of fresh water, 80 L of grey water, a 17 L cassette), the fresh water lasts 2.4 days, the grey tank 2.5 days, the cassette 3.5 days and the battery 14 days: the stay ends after 2.4 days, for lack of fresh water.
How many litres of water for a week in a campervan?
For 2 people, count ≈ 161 L on a frugal routine (dishes in a bowl, no shower on board) and ≈ 322 L with one quick shower per person per day, plus 20% in summer. The 4 L per person per day of the Nomad score's van reference covers drinking and cooking only.
What fills up first: the grey tank or the cassette?
Mostly it depends on showers. For 2 people in July, with a quick shower every other day, 80 L of grey water last 2.5 days and a 17 L cassette 3.5 days: the grey tank overflows before the cassette. Without showers on board, the grey tank lasts 4.4 days and the cassette is full before it.
How long does a campervan battery last without charging?
Indefinitely while the panels cover consumption; otherwise, usable capacity divided by the day's deficit. 100 Ah of lithium gives 1,020 Wh usable: with 200 W of panels in July (Southern France, Italy, Croatia, northern Spain) and 1,275 Wh used per day, the deficit is 74 Wh, i.e. 14 days. That figure is fragile: the panels already cover 94% of the load, and with 10% less sun it drops to ≈ 5.3 days. In December, same place: 0.6 days.
Go further
- Solar and battery calculator: your appliances, your output month by month
- Water Self-Sufficiency in a Van — The Complete 2026 Guide (Usage, Filtration, Maintenance)
- Grey water and toilets: the van's outlet circuit
- Van Self-Sufficiency: Power, Water, Food — the Complete Route-by-Route Breakdown
- Charging without sun: alternator, shore, generator
- Vans and motorhomes: reference needs and autonomy score
Beyond the tanks: your full Nomad score
The questionnaire adds your destination, food and safety, and works out the four pillars of your trip's autonomy score. Free, no account.
Calculate my Nomad scoreThe score is an indicative estimate based on averages: it does not replace preparing your trip.