Boondocking Days Calculator

How long will an RV fresh water tank last?

Divide the tank by what the crew draws in a day. For two people who take short showers, wash dishes in a basin and don't try very hard to save, that's about 8.0 gallons a day, or 4 per person. A 52 gallon tank is 6.5 days on that; 40 gallons is 5.0. The common tank sizes against one, two and four people:

"Normal" use: 3.5 navy showers a week, basin dishes, 3 flushes a day, for 4 gal per person per day; 8.34 lb per gallon. A pump can't draw the very last of a tank, so round down.

Those are fresh-tank days. Whether you get to use them depends on the gray tank, which is the next section, and on how much of the fresh tank you drove in with. At 8.34 lb a gallon, a full 52 gallon tank is 434 lb of payload, which the loaded weight calculator counts against your GVWR, and plenty of rigs travel a third full and top up at the last spigot.

How much water do you use a day boondocking?

Less than any house figure and more than you'd guess, and the shower decides most of it. The three presets, per person per day, with where each gallon ends up:

Normal = 3.5 navy showers a week (3 gal); careful = 1.75; frugal = showers at the bathhouse. Toilet at 0.3 gal a flush, our planning figure: Dometic rates its 310 gravity toilet at one pint a flush, and holding the pedal to rinse the bowl uses more. Plus 0.3 gal a day of what the body adds. Edit any line on the calculator.

A running shower every day is the line that moves the total most: two people showering with the water on turn 8.0 gallons a day into 25.0. The water heater calculator shows how many minutes of that shower the tank can heat. Match the preset to what you do, then edit the shower line; nothing else moves the number much.

Why does the gray tank fill before the fresh tank empties?

You can add fresh water and you can't subtract gray. On paper a 40 / 30 / 30 gallon rig with two aboard runs out of fresh first: 5.0 days against 6.0 for gray, since only 5.0 of the 8.0 gallons a day drain to the gray tank. Then you bring jugs, or a bladder, or fill from a spigot on the way back from town, and the fresh side stretches while the gray side keeps filling at the same rate:

40 gal fresh, 30 gal gray, two people at normal use (8.0 gal/day drawn, 5.0 to gray).

That's the mechanism behind the forum rule that gray ends the trip. Gray doesn't fill faster; it's the one tank you can't do anything about without moving the rig or hauling a portable tote. The result panel names the limiting tank for your numbers and, when it's gray, says how many days of fresh you're leaving on the table. The fixes are all upstream: shower at the bathhouse, catch dish and shower water in a basin where local rules let you spread it, and don't let the shower run while the water heats.

What size fresh water tank do I need?

Days you want, times what the crew draws, and the same arithmetic for gray and black, because a big fresh tank with a small gray tank is a big fresh tank you can't use. Switch to "tanks for N days" above and the calculator prints all three, and how far your rig is from each. The reference numbers:

Normal use, no jugs. Shopping: compare to the floor plan's tank sizes on the spec sheet, which are nominal; the usable volume is a little less on every tank.

A fresh tank is part of the floor plan, so the practical version of this question is "how many gallons of jugs do I need for the week?" The reverse mode prints that as the fresh shortfall, in gallons and in pounds, since 167 lb of jugs in the truck bed is a payload question. For gray, the shortfall is either a tote or a dump run on the day the tank fills, and the result says which day that is.

How do you make RV water last longer?

In order of gallons saved: shorten the shower (or move it to the bathhouse, which is the "frugal" preset and takes two people from 8.0 to 3.0 gallons a day), catch the cold water while the shower heats and use it for dishes, wash dishes in a basin and rinse with a spray bottle, and flush with the pedal held for a second instead of three. Drinking water from a separate jug keeps the fresh tank for washing and means an aging tank matters less; a tank that has sat a while gets the bleach-and-rinse treatment before it's trusted again. On the gray side, a basin under the sink that you carry outside, where the campground or the land manager allows it, is the only thing that empties gray without moving. And the sensors lie: a gray sensor reads full from soap film and a black sensor from paper, so trust the day count above over the panel, and trust a full-sounding sink drain over both.