Dethleffs c.core concept: the motorhome that recycles its own shower water

A motorhome that turns last night's shower back into tomorrow's tap water. That is the headline idea in the Dethleffs c.core, a concept shown at Caravan Salon Düsseldorf 2026, which ran from 28 August to 6 September. It is a concept in the proper sense: Dethleffs has no production plan for it, you cannot order one, and it is not coming to a dealer near you. But the thinking behind it deserves a calm look, because it goes after the limit most people hit first when they try to stay off grid for a week. Not electricity. Water.

What Dethleffs put on the stand

The c.core is a one-off built to show where Dethleffs thinks motorhome construction and living could go. New Atlas describes the base as a lightly ruggedised Volkswagen Crafter chassis. On top of that sits a habitation body built around a new structural system Dethleffs calls Necto, with a curved, monolithic shape and flush windows, doors and hatches. New Atlas and RV Pro both describe the concept as bringing biomimicry, solar expansion and closed-loop recycling together in one vehicle.

The headline features, as reported by Reisemobil International and promobil:

• Grey water from the shower and sinks is treated back to fresh water, then passed through two further filter stages to what Dethleffs calls germ-free pure water. promobil says the system can run a complete season without a filter change.
• A deployable solar array Dethleffs calls the Solarblume (solar flower), giving up to 600 W.
• A Necto body built from 0.8 mm aluminium sheets, which Dethleffs' first calculations say could save about 25 to 45 kg in the body of a seven-metre motorhome.
• Insulation made from about 1,800 recycled PET bottles.
• Four solid-state lithium batteries with about 5.2 kWh of storage (400 Ah).
• Truma heating running on HVO, a renewable diesel.

Autoevolution lists the same 600 W of solar and 400 Ah battery. That is the shape of it: a smart, well-equipped van whose most interesting trick happens underneath the shower tray.

Why water, not power, ends most off-grid stays

Ten years ago the thing that sent you back to a hook-up was a flat leisure battery. Lithium batteries, decent solar and a battery-to-battery charger have largely fixed that. Plenty of ordinary vans now run a compressor fridge, lights, a diesel heater and a laptop for days without a mains cable, and when the sun is out the battery looks after itself.

Water does not work like that. There is no panel on the roof that makes it. You leave with a full fresh tank and an empty grey tank, and every shower and every washing-up bowl moves litres from one to the other, so the trip ends when the fresh tank runs dry or the grey tank fills, whichever comes first. Either way, the trip ends at a service point.

Water is also heavy. A litre of it weighs a kilogram, so carrying more is not free. Every extra litre of fresh water comes straight out of your payload, and on a van plated at 3,500 kg to stay within a category B licence, payload is often the scarcest thing you own. Makers differ in how much water they count in the mass in running order figure, so check the definition on the maker's own spec table before you assume a full tank is already accounted for.

Put those two facts together and you see why the c.core idea is more than a party trick. If the water you use for a shower could go round again, you would not need to carry more of it. You would just use the same litres several times over.

How the c.core's water loop is meant to work

The concept handles grey water, which is the run-off from the shower and sinks. Toilet waste is a separate matter and is not part of the reported system. According to Reisemobil International and promobil, the grey water is first treated back to fresh water, then passed through two further filter stages to reach what Dethleffs calls germ-free pure water. promobil adds that the filters are meant to last a complete season without being changed.

Dethleffs adds that the technology has its roots in crewed spaceflight and recommends changing the filters once a year. A concept does not have to answer the questions a production van would. Three stand out:

1. What goes in. Shower water carries soap, shampoo, skin and hair. Sink water carries grease and food. Any treatment system has to cope with whatever people put down the plughole, and a production version would need to tell owners which soaps and cleaners it can cope with.
2. What it costs in energy and weight. Pumps and filtration draw power and take up space. On a concept with 5.2 kWh of battery and 600 W of solar that may be comfortable, but the balance would look different on a smaller van.
3. Whether people will drink it. Plenty of people will balk at drinking water that started out in the shower tray, however good the filters are. The science of water treatment is well understood; the feelings around it are not so easily filtered.

None of this is a criticism of the concept. It is exactly the sort of question a show vehicle exists to raise. A van that could safely give its shower water a second and third life would change the arithmetic of a long wild stay more than any battery upgrade has.

The rest of the concept, and what it is for

A lighter, more recyclable body

The Necto structure is built from 0.8 mm aluminium sheets, and Reisemobil International and promobil put the saving at about 25 to 45 kg. That is a modest number on its own, but it is worth translating: 45 kg is the weight of 45 litres of water. A lighter shell is not just about handling, it is about what you are allowed to carry.

Insulation from recycled bottles

The insulation is made from about 1,800 recycled PET bottles. Fibre insulation spun from recycled plastic is already an established material in building and clothing, so this is less a new invention than a new place to use one.

Solid-state batteries and a solar flower

Four solid-state lithium batteries give about 5.2 kWh, or 400 Ah. That capacity is not unusual for a well-specified van today; the chemistry is the new part. The deployable Solarblume array gives up to 600 W when opened out, which is a neat answer to the oldest problem with van solar: the roof is only so big.

Heating on HVO

The Truma heating runs on HVO (hydrotreated vegetable oil), a renewable fuel that can be used in place of fossil diesel. On a concept that is about closing loops, warming the van without adding fossil carbon fits the brief.

Which ideas are closest to vans you can buy

Concepts are usually a mix of things that are nearly here and things that are decades off. Here is a fair sorting of the c.core's ideas, from nearest to furthest.

Nearest: lighter construction and recycled materials

Habitation bodies already lean on aluminium skins and composite panels, and makers compete on weight every model year because payload sells. A new structural approach like Necto is the sort of thing that could arrive in production without much fanfare, and recycled insulation could follow the same quiet route. Neither needs a change in the rules or in how owners use their vans.

Within reach: HVO heating

HVO is already sold in the UK by some fuel suppliers, so the fuel exists. What matters for you is whether the heater fitted to your van is approved to burn it, and that is a question for the heater's maker, not something to assume. If you have a diesel-fed heater and HVO is available near you, ask the manufacturer in writing before you try it, and keep the answer with your handbook.

Also within reach: solid-state batteries

Most leisure lithium fitted to vans today is lithium iron phosphate, which is proven, affordable and safe. According to New Atlas, the c.core stores its power in Renogy's Super Slim Solid State lithium batteries, and Renogy already lists a 12 V, 104 Ah Super Slim Solid State leisure battery, so this is a newer kind of battery rather than a lab project.

Furthest: recycling shower water into drinking water

This is the c.core's headline idea and the one with the longest road ahead. Turning grey water into something a maker is prepared to call drinkable means proving it, testing it, taking responsibility for it, and persuading owners to trust it. A simpler halfway house, recycling grey water for toilet flushing or for the next shower rather than for the kettle, would be far easier to deliver and would still stretch a fresh tank a long way. Dethleffs' concept goes straight to water it describes as purer than ordinary drinking water, but the halfway house is the version most likely to reach a real van first.

What you can do about water today

You do not need a concept van to make your fresh tank last longer. Most of the gains come from habit, not hardware.

• Shower like a sailor. Wet, tap off, soap, tap on, rinse. A low-flow shower head with a pause button makes this painless and is one of the cheapest upgrades in the hobby.
• Wash up in a bowl, not under the tap. A single bowl of hot water does a day's dishes; a running tap does not.
• Use the campsite's facilities when you have them. Showering in the site block when you are on a pitch keeps your own tanks for the nights when there is nothing else.
• Carry a backup container. A folding or rigid container of a size you can lift into a water point lets you top up where you cannot get the van close to a tap.
• Know your service points before you go. Aires, motorhome stopovers and some campsites offer fresh water and grey disposal to non-residents, sometimes for a small fee. Plan around them the way you plan around fuel.
• Empty grey water only where it is allowed. Tipping it on the ground at a campsite or lay-by is the quickest way to get motorhomes banned from somewhere good. Use the drain provided.
• Keep the fresh tank clean. If you drink from the tank, sanitise it at the start of the season and after any long lay-up, and consider an inline drinking-water filter at the tap. Recycled or not, water is only as good as the tank it sits in.

The bottom line

The Dethleffs c.core is not a van you can buy, and nobody should read a show concept as a promise. What it does well is point at the right problem. Batteries and solar have made power a solved question for most touring; water is the limit that remains, because you cannot make it, you have to carry it, and it weighs a kilogram a litre. The lighter body, the recycled insulation and the HVO heating could all reach production vans without anyone noticing. Solid-state leisure batteries, the kind New Atlas says the c.core uses, are already listed by Renogy. Recycling shower water into something you would put in a kettle is the furthest away, and the most interesting, because if it ever works in a way owners trust, it would change how long a motorhome can stay put more than anything since lithium. Until then, a good shower head and a bowl for the washing-up will stretch your tank further than you might think.