When you camp without hookups, the size of your RV’s tanks decides how long you can stay. The fresh water runs out, the gray tank fills with sink and shower water, or the black tank fills from the toilet, and whichever comes first ends the stay. This calculator finds that limit.
The three tanks
- Fresh water supplies the sinks, shower and toilet.
- Gray water collects drain water from the sinks and shower.
- Black water collects toilet waste and flush water.
Typical travel trailers and motorhomes carry 30 to 100 gallons of fresh water and gray and black tanks of 20 to 50 gallons each.
How the days are computed
fresh days = fresh tank ÷ (people × water per person per day)
gray days = gray tank ÷ (people × (water per person − toilet water) × 90%)
black days = black tank ÷ (people × toilet water per person)
The 90% accounts for water that is drunk or used in cooking rather than drained. Two people using 6 gallons each a day empty a 40-gallon fresh tank in 3.3 days. Their 35-gallon gray tank would fill in 3.9 days and their 30-gallon black tank in 15 days, so fresh water is the limit.
How much water do people use?
- Very careful boondocking: 2 to 3 gallons per person a day, with navy showers, paper plates and a dishpan.
- Moderate: 5 to 8 gallons, with short showers every day or two.
- Like at home: 15 gallons or more; tanks last only a day or two.
Toilet flushing usually adds about 0.5 to 1.5 gallons per person per day to the black tank.
Making the tanks last
- Take navy showers: wet, turn off the water, soap, rinse.
- Wash dishes in a basin and reuse the rinse water, or use a campground’s facilities when available.
- Carry extra fresh water in jugs, and use a portable waste tank to empty gray water at a dump station.
- Use campground restrooms when you can to save the black tank.
- Bring drinking water separately if you prefer not to drink from the tank.
Never dump gray or black water on the ground; use a dump station. Rules vary by park and public land agency.