Van Water System Calculator
Figure out how much fresh, grey, and black water capacity you actually need — and what system fits your build.
🧭 Travel Profile
Navy showers, some dishes, normal cooking (~4–6 gal/person/day)
🚿 Your Setup
≈ 6 gal per shower at 2 GPM
Recommended baseline is about 3/4 gallon per person per day for drinking.
📊 Results
Fresh Water Tank
100 gal
Covers 7 days for 2 people at moderate usage
Bigger than a typical single van tank — plan on two tanks or refilling more often.
Grey Water Tank
80 gal
Sized to match your fresh tank minus drinking water
Black Water Tank
Not needed — no flush toilet selected
Daily Usage
11.50 gal
With Buffer (+15%)
13.20 gal
Days Between Refills
7
Full Tank Weight
834 lbs
Est. Total Cost
$540 – $950
💵 Estimated System Cost
Estimate only — actual cost depends on brand and install complexity.
💡 Tips
- A conservative van lifer typically uses 2–6 gallons per person per day; full-hookup RV habits can run 20+ gallons per person per day — know which one matches your lifestyle before sizing tanks.
- Showers are usually the single biggest water user in a van — a 3-minute shower at 2 GPM uses about 6 gallons.
- Your grey tank should generally match or slightly exceed your fresh tank, since almost everything you use ends up as greywater (except what you drink or use to flush).
- If you don't have a flush toilet, you don't need a black tank — cassette and composting toilets use little to no water.
- Water weighs 8.34 lbs per gallon — a full 30-gallon tank adds about 250 lbs to your van.
- Oversizing your tank isn't free: bigger tanks cost more, take up more space, and add weight even when not full. Size for your actual refill rhythm, not worst-case scenarios.
- Sanitize fresh water tanks regularly (a diluted bleach flush every few months) and don't let water sit more than about two weeks for drinking quality.
💧 Need a tank or plumbing parts? Browse van water system gear — fresh and grey tanks, fittings and hose.
🔌 Need a pump? Shop the Shurflo 12V water pump — the go-to demand pump for van builds.
🚽 Comparing toilet types? Read our toilet cost comparison guide.
🔧 Planning the whole system? Read the van water system guide.
Or check out our full gear recommendations.
❓ Water System FAQs
How much water does a van need per day?
Most van lifers use 2–6 gallons of water per person per day. Minimal setups without a shower use about 2 gallons, while full hookup habits with daily showers and dish washing can run 10–20+ gallons per person per day.
What size grey tank do I need in a camper van?
Your grey tank should generally match or slightly exceed your fresh tank, since almost all the water you use ends up as greywater — everything except what you drink or flush.
Do I need a black water tank in a van?
Only if you install a flush toilet. Cassette, bucket, and composting toilets use little to no water and store waste internally, so no black tank is needed.
How much does a full water tank weigh?
Water weighs 8.34 lbs per gallon, so a full 30-gallon fresh tank adds about 250 lbs to your van — plus the weight of a full grey tank.