How much water does a campervan need? Tank sizes, placement and weight
· 6 min read
“How big a water tank do I need?” gets answered in forums with a number — usually somebody else's number. The correct answer is an equation: litres per person per day, times people, times days between refills. Do that arithmetic first, because the tank you choose is also the heaviest single item in the build, and where you put it is an axle-load decision disguised as a plumbing one.
What a day of van life actually uses
Measured with a jerry can rather than guessed, daily consumption breaks down roughly like this per person:
| Use | Litres per person per day | Notes |
|---|---|---|
| Drinking + cooking | ~3–4 L | More in summer; tea and coffee count |
| Dishes | 3–5 L | Per wash-up, not per person — two basins and discipline |
| Hand washing, teeth, wipe-downs | 2–3 L | The quiet accumulator |
| Navy shower (wet, off, soap, rinse) | 6–10 L | Needs a low-flow head and resolve |
| Quick normal shower | 15–25 L | What most people actually take |
Now run the totals. A couple on a weekend trip, no shower: two people × two days × ~7 L (drinking, cooking, hands) plus three or four wash-ups — roughly 30–40 L. The same couple off-grid for a week with a shower each every other day: base consumption of ~100 L plus six or seven showers at 15 L+ — comfortably past 150 L. That factor-of-four spread is why there is no single right tank size, only a right size for how you travel.
Fresh and grey pairings that fit real builds
Grey capacity matters as much as fresh: on most European aires and many wild spots you cannot legally dump grey water on the ground, so a full grey tank ends the stay exactly as firmly as an empty fresh one. Sizing grey at 60–80% of fresh works because some fresh water is drunk, not drained.
| Build type | Fresh | Grey | Refill rhythm |
|---|---|---|---|
| Weekender, no shower | 40 L | 25 L | Fill at home Friday, dump Sunday |
| Couple touring, navy showers | 70–100 L | 50–70 L | Every 3–4 days |
| Full-timer with a real shower | 120–150 L | 80–100 L | Every 3–5 days, planned around service points |
Resist the instinct to size up “just in case”. Water you carry and never use is pure payload tax, and unlike a heavy cabinet it moves.
Weight and placement: the part plumbing guides skip
Water is the densest thing you will install: 1 L = 1 kg, exactly and always. A 150 L fresh tank plus a fullish grey tank is 200 kg+ — often more than the entire furniture set, and a large bite out of the payload budget. Worse, it is 200 kg that varies between zero and full and sloshes while you brake.
Placement therefore has two rules. Low: every kilogram above the waistline raises the centre of mass and worsens body roll; tanks belong on the floor or under it, never in an overhead locker run. Central: 100 L sitting behind the rear axle acts as a lever — it loads the rear axle by more than its own weight and actually unloads the front, which is steering and braking. Between the axles, the same 100 L splits benignly across both. If the rear axle margin is already thin (see what conversions really weigh), tank position is the cheapest fix available, because moving a tank is free at the design stage and miserable after.
Underslung versus internal is the same trade-off from another angle. Underslung tanks free up garage space and keep the mass as low as physically possible, but they sit in the airstream and freeze first — usable three seasons, or four with tank heaters and insulated pipe runs. Internal tanks live inside the heated envelope and shrug off frost, but they eat the exact under-bed volume the garage wanted, and every litre must fit around wheel arches and furniture. Most cold-climate builds end up internal fresh, underslung grey: grey water freezing is an inconvenience; fresh water freezing is a dead system.
The practical layer
Winterising: if the van sleeps outside below freezing and the tanks are not inside the heated shell, drain everything — tanks, pump, low points in the pipe runs, and the water heater if fitted, since a cracked calorifier is the classic spring surprise. Internal tanks in a van that stays heated (or gets fully drained between trips) skip the ritual, which is a real argument for them in northern Europe.
Filling logistics: a single 120 L tank with one inlet assumes you can park next to a tap and reach it with a hose. Much of the time you cannot. Two smaller tanks — or one tank with a wide jerry-compatible inlet — let you ferry water in 20 L cans from a fountain, a petrol station, or a friendly café, which in practice extends off-grid range more than an extra 30 L of capacity would. Some builders run a 20 L removable drinking container plus a fixed washing tank for exactly this reason.
On hardware: a 10 L/min 12 V diaphragm pump with a small accumulator tank gives steady pressure without the pump cycling on every hand-wash — fit the accumulator, it costs little and saves both power and irritation.
Design it as ballast, not plumbing
Pick the capacity from the consumption table, then treat placement as seriously as the bed position — because at 1 kg per litre, it is a furniture decision. The useful test is to see the numbers move: place the fresh and grey tanks in your layout and watch the front/rear axle split change as they fill. VanPlot simulates full and empty tanks in the weight readout, so the “behind the axle” mistake shows up as a number before it shows up on a weighbridge — free in the browser, and cheaper than a re-plumb.