Should you carry water and fuel in jerry cans or a built-in tank?

What decides it?

How often you use it, and for how long. Water for drinking, cooking and washing is drawn on several times a day, so every can is lifted, carried, poured and stowed again, over and over. Reserve fuel is drawn on a few times a year, if that. A tank earns its cost by removing handling, so it pays back fastest on the supply you touch most.

Coen Wubbels and Karin-Marijke Vis, who lived in a 1984 Land Cruiser BJ45 for more than twenty years, put the rule in one sentence: "For a 1- or-2-year journey, we'd stick to containers for budget reasons." Once the trip had no end, the tank, filters and sink were worth it. It took them twelve years to build one, and they say they should have planned it before leaving.

How much does it weigh, and where should it go?

Water weighs a kilogram a litre, which the USGS gives as 1.000 grams per cubic centimetre at 4 °C and barely less when warm. Diesel is lighter, 0.820 to 0.845 kg a litre under the European EN 590 standard, and petrol lighter again at 0.720 to 0.775 under EN 228. Container weight comes on top.

Low and between the axles is the best place for it, and the roof is the worst. On the roof it raises the centre of gravity, adds to the roof's own load limit, and loads rack mounts that were never designed for it. The BJ45's owners found that out the slow way: "Roof bars, but also window bars broke and were welded on numerous occasions", until the reserve diesel moved to a tank under the truck. Behind the rear axle it lightens the front and sags the rear. Kristen Bor of Bearfoot Theory found her second van sagging with 25 gallons of water and a heavy battery bank in the rear garage.

However you carry it, it counts against payload. A full 100 litre water tank and two full 20 litre jerrycans of diesel come to about 135 kg before the containers, which is a passenger's worth of weight on many trucks.

What does a water tank actually cost?

Less in materials than people expect and more in everything else. The BJ45's tank started as two food-grade stainless tanks bought from a scrapyard in Venezuela for the equivalent of $20. Turning them into one 100 litre tank and its brackets took a shop crew "about five days of cutting and welding", and the space for it only existed because the old exhaust, which ran diagonally under the floor, had broken and been replaced with a short side exit.

Then the tank needs a system. Theirs has a coarse sediment filter where the hose enters the body, a pump, a pressure tank, a sediment filter and a UV filter on a separate drinking tap, a sink, and a hand shower. It all had to fit the rear corner so it would not cost packing space, and the compromise that made it fit means "hoses would bend 45 degrees every time we would need to access the water system's core." The pump keeps running into a leak, so they added a switch to cut its power. They fill the tank through a funnel made from a cut-up bottle, and there is no level gauge.

What goes wrong with a tank in winter?

It freezes, along with the hose and filters that feed it, if any of them sit outside the heated space. The BJ45's owners had travelled mostly in the tropics and never planned for it. In winters in Japan, Russia and Central Asia they "run the tank dry, close off the system and go back to carrying 2×20 liter jerrycans inside the vehicle."

Bearfoot Theory's vans learned the same lesson from the other side. On the first van, "my exterior 15-gallon tank is unusable in winter, limiting me to the 10-gallon tank inside." On the second, the whole plumbing system went inside the van so nothing could freeze, and the third keeps its tank in a cabinet inside the heated space. If you travel in snow, an inside tank or a couple of cans you can bring indoors will outlast an underbody tank.

Fuel: a bigger tank, cans, or both?

Start from range, not litres. Coen Wubbels's advice to a reader planning a fuel system: "I think you need to think about range instead of liters. What distance feels good to you?" Work out how far you need to go between fuel stops on the route, multiply by consumption loaded and off-road, which is higher than on the highway, and add a margin.

Then ask how often you would use the extra. The BJ45's 85 litre main tank gave 600 to 750 km, and in two decades the reserve was needed a handful of times: the Persian Gulf coast of Iran, Patagonia, south-west Bolivia and the Bartang valley in Tajikistan. For a reserve used that rarely, cans are cheap and do no harm sitting empty, but full ones on the roof broke that truck's rack. A second tank underneath, fitted in Bolivia in 2010, took the weight down, and two cans stayed on the roof for the rare day they were needed.

Cans also do something a tank cannot: carry fuel from a station to a vehicle that ran dry, or to a stove. Keep at least one. Carry it outside the cabin, and check the rules where you travel. In the UK, for example, the Health and Safety Executive caps petrol in spare containers at 30 litres in no more than two suitable containers, and its definition of premises includes motor vehicles.

What makes a good water can?

One small opening that closes tightly and a narrow neck, so water pours out without a hand or a cup going in. That is the CDC's description of a safe household water container, and it suits a vehicle too. Use a container made for drinking water, or one bought new and never used for anything else. The CDC says never to store water in one that has held fuel, solvents or other chemicals.

Clean and sanitise it regularly. The CDC's method is to wash it, then shake it with 5 mL of unscented household bleach (5 to 9 percent sodium hypochlorite) per litre of water so the solution touches every inside surface, wait at least 30 seconds, pour it out and let it air-dry. The same applies to a tank, which is harder to reach inside, and is one more reason to plan the access before you build it.

Good cans can be hard to find away from home. The BJ45's owners could not find a second heavy-duty water can outside Europe and made do with a red plastic fuel can of the kind used on boats. Buying the cans you need before you leave is cheaper than improvising later.

How do the builds on this site carry theirs?

Every one of them ended up with the water low and inside or between the axles. The cans that survived are the ones used rarely: reserve fuel on the BJ45's roof, and the winter water cans that come out when the tank is drained.