Biosphere City : The water and energy efficient shower

BIOSPHERE EXPERIENCE

https://wiki.lowtechlab.org/wiki/Biosph%C3%A8re_Urbaine_:_La_douche_%C3%A9conome_en_eau_et_en_%C3%A9nergie/en

Dernière modification le 13/10/2025

Difficulty

Medium Medium

Duration

2 day(s) day(s)

Cost

50-150 EUR (€)

Description

Taking a hot shower is a real pleasure, but it has a significant environmental impact. A mist shower allows you to enjoy the same pleasure while reducing water consumption and providing a new showering experience. Instead of water flowing freely over your body, it is gently misted. The solar-powered water heater ensures the ideal water temperature with low energy consumption and minimal heat loss. This tutorial covers the steps involved in making an energy-efficient hot water tank.

Summary

Douche, Econome, Brumisation, Chauffe-eau

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Introduction

Project

The BIOSPHERE EXPERIENCE association is experimenting on sustainable and desirable futures in which humans live in symbiosis with other living species. In 2024, Caroline Pultz & Corentin De Chatelperron spent four months experimenting with what a low-tech lifestyle in an urban environment might look like: a lifestyle without waste, reducing water consumption ten-fold, meeting the UN's 2050 targets for greenhouse gas emissions, while remaining desirable and accessible to all. Armed with experts, volunteers, and interns, they imagined and designed a forward-looking ecosystem-apartment called Biosphère Urbaine, located in the Paris region in Boulogne-Billancourt. To complete the ecosystem, their colleague Emma Bousquet-Pasturel has set up a vast citizen support network around the apartment. At the same time, Emma has been tasked with launching a participatory science program bringing together hundreds of French and international citizens to test the low-tech systems of the apartment-laboratory in their own homes.

This tutorial is for a low-tech module of the apartment-laboratory , designed as part of the experiment in Boulogne-Billancourt.

To access the tutorial for the participatory science program: Sciences Participatives : La douche à brumisation

The water and energy efficient shower :

The experimental apartment created for the Urban Biosphere has all the features of a “standard apartment” and is equipped with everything needed for everyday living. This allowed Caroline and Corentin to design and test various devices for the kitchen, toilet, and shower.

This tutorial will focus mainly on the bathroom and the topic of efficient showers. This topic takes into account both water consumption and energy consumption for water heating.

The hot water tank:

It has been shown that cold showers significantly improve sleep quality, release happiness hormones, and reduce muscle inflammation after exercise thanks to their temperature. Contrary to popular belief, cold showers do not weaken the immune system — quite the opposite, in fact!

But since it is always nice to take a hot shower after a hard day and it also has its own benefits and uses, we have developed an economical heating and storage system.

A brief history of the system presented in this tutorial : In residential housing, heating accounts for the largest energy expenditure, followed by hot water (i.e. water heaters). According to ADEME, “Domestic hot water accounts for approximately 35% of household water needs and more than 12% of energy consumption.”

Finding a solution that would allow residents to continue enjoying hot showers with less impact was therefore essential. The solution found and tested in the Biosphere apartment is twofold: first, reducing the volume of water to be heated, and second, manufacturing a hot water tank that uses solar energy and has low heat loss.

The hot water tank was made by Corentin, Smat, and Frédéric especially for the experiment. It has a capacity of 2 liters, is very well insulated, heated by a 150W resistor, and powered by the Biosphere's solar panels.

But why 2 liters? First and foremost, Caroline and Corentin identified their water needs for showering. This depends on each individual, their body type, hair type, health (need for a hot bath to warm up the body or a cold shower after exercise), etc. For the amount of water: Corentin needs 3L (short hair), Caroline 5L (medium-length hair). They are the same height (around 5'8"). So they decided on a 5L shower. For the temperature: after multiple tests, they concluded that 2L of water at 85°C combined with 3L of cold water was ideal for them (this gives water at around 46°C).

Improvements to consider: a second thermostat and a 3-position switch would be useful to have a choice between 2 temperatures. In winter, we need it to be warmer (thermostat set to 85 degrees), in mid-season it could be somewhere in-between (for example 65 degrees), considering that in summer it is not necessary to heat it.

Improve the system so that the tank heats up when the batteries are full, so that the energy surplus produced by the solar panels can be stored as heat instead of being lost.

User feedback: Very pleasant once you get used to adjusting the nozzles.

Benefits of the machine:

The energy-efficient water heater has many advantages:

• Use green electricity generated by solar panels. The aim here is to maximize the apartment's energy independence and therefore optimize energy storage in the batteries in order to have a low-consumption system.
• Reduce energy losses and convert most of the electricity into heat to warm water.
• Reduce household water consumption, thereby reducing environmental impact as well as water and electricity bills.

This tutorial describes how to build an energy-efficient water heater in three main steps, along with a quick user guide to help you get started. The model presented in the tutorial can be adapted, modified, and improved according to your preferences, materials, and skills.

Youtube

Materials

This is a comprehensive list of materials. If you already have some of these items, we recommend buying second-hand and adjusting their diameters and sizes throughout the tutorial.

• Water tank:
  • 1 2L bottle (in our case: a returnable stainless steel Chocapic box)
  • 1 gasket (Le Parfait jar type)
  • Wooden board
  • PLA sheet
  • Aluminum-coated bubble wrap insulation
  • Plant fiber insulation
  • High-temperature aluminum tape
  • Threaded rod
  • Nuts
  • Washers
• Heating element
  • 3 transparent 12V 50W patches
• Electrical/sensors:
  • 85-degree thermostat
  • 2-input terminal block
  • Electrical wires
• Water connectors:
  • Standard plumbing fittings
  • Food-grade plumbing sealant
  • Plumbing pipe
  • Valve

Tools

This is a comprehensive list of tools to adapt based on what you already have.

• Cutter
• Jigsaw
• Router
• Drill
• Scissors
• Measuring tape
• Hacksaw or grinder
• Protective gloves
• Safety glasses

Step 1 - Material collection and purchase

Depending on the level of finish, the adaptation of the model, and the use of recycled materials, we estimate the cost of an energy-efficient water heater to be between €50 and €150.

Before making your purchases, we strongly recommend that you read the entire tutorial, as the list of materials can be adapted depending on what you have at home.

For tools and equipment, we encourage you to check out places such as recycling centers or tool libraries before buying anything. You may find what you need there, as well as advice from enthusiasts.

Step 2 - Tips and precautions

Before starting fabrication, ensure that your workspace is secure and that your tools are stored efficiently.

• Use tools that are in good condition and suitable for the work to be done.
• Read the tool instructions carefully and pay attention to the pictograms on the packaging.
• Work in a clear, well-ventilated, and well-lit area.
• Wear the necessary protective equipment: gloves, shoes, goggles, clothing, helmet, protective mask, earplugs (earmuffs/earplugs), etc.
• Unplug power tools and close products when not in use.
• Ask for help if you need to handle heavy loads (tools, materials, etc.).

Regarding specific precautions for hot water tanks, here are the regulations in France:

Art. 36 of the decree of June 23, 1978, relating to fixed installations intended for heating and supplying domestic hot water to residential buildings, offices, or buildings open to the public (ERP))

This article states that water must be kept at a temperature above 50°C in the distribution system for 24 hours prior to use in order to reduce the risk of bacterial growth. However, at the outlet, the water from the shower that comes into contact with the body must be below 50°C to prevent burns.

This is not possible with the mist shower, as the mist must be released at a higher temperature. That is why it is important to have 30 cm between the nozzle and the skin. In addition, as you shower, the water gradually cools down gently.

This is a non-exhaustive list of tips and precautions.

Step 3 - Sizing according to your needs

Sizing the hot water tank is an important step that will ensure a sufficient volume of hot water according to usage, the number of people in the household and the type of washing desired.

For the purposes of this tutorial, we are assuming a requirement of 5 litres and a 2-litre hot water tank.

Here's how to size it :

• Etape 1 : Set the maximum amount of water for one shower

Person	Water quantity	Max quantity
Caroline	5L	5L
Corentin	3L
Person 3	0L

Here is a table showing the recommended amount of water depending on hair length (for washing with a mist nozzle) :

Hair length	Water quantity
Short hair	3L
Medium-length hair	5L
Long hair	8L
Shower without hair washing	2,5L

(Values can be updated based on your own experience.)

• Etape 2 : Set the volume of the water tank

Here, the desired outlet temperature will greatly influence the volume of the tank. In fact, in the case of this tank, the objective is to heat a small volume of water to a temperature of 85°C and mix this volume with a quantity of cold water to obtain the desired temperature. To obtain the exact values, thermodynamic calculations would need to be performed, including various factors that are specific to each manufacturing process.

Note: Cold water from the mains gradually mixes with hot water from the tank as you shower. It is very hot at first, then gradually cools to room temperature.

For this tutorial, the data presented has been simplified and is based on feedback and tests carried out by Caroline and Corentin. They drew on recommendations from various sources, including NASA's SkyLab Shower and Jonas Görgen's Mist Shower. To sum up: the ideal temperature for a pleasant and relaxing shower is between 37°C and 40°C. Above 42°C, the water becomes too hot, which can irritate the skin, cause redness, or even increase blood pressure. In the specific case of misting, this temperature should be slightly increased because when water is misted, it loses heat mainly due to heat exchange with the air: if the ambient air is colder than the misted water, it absorbs heat. For example: if the ambient air temperature is around 20°C with moderate humidity, the misted water can quickly lose 5 to 10°C. If the air is very dry or much colder, the loss can be even greater. For a more accurate assessment, it would be necessary to know the ambient temperature, relative humidity and misting characteristics. Based on tests for a water volume at 100°C and to obtain an outlet temperature of around 45°C, here is the calculation: Cold water volume = Hot water volume x 3/2 Total volume = Cold water volume + Hot water volume Hot water volume = Total volume x 2/5 Here, the volume of hot water corresponds to the size of the water tank.

In the Biosphere's case :

Total volume = Cold water volume + Hot water volume = 5L

Water tank size = Total volume x 2/5 = 5 x 2/5 = 2L

For example, for a hot water bottle for a person with long hair, you need :

Total volume = Cold water volume + Hot water volume = 8L

Water tank size = Total volume x 2/5 = 8 x 2/5 = 3.2L

Step 4 - Preparation of the heating core

The heating core of this energy-efficient water heater is the area that concentrates all the technology of this system. It is the part that must be made with the most care in order to guarantee both watertightness and overall safety.

In order to make the tank that will hold the heated water, you need to use a watertight container (or one that can be made watertight) and drill holes for the water inlet and outlet.

The choice of material for the container is important because storing water can cause corrosion or rapid degradation of the material if it is not suitable.

Then use standard plumbing fittings to connect the pipes and fittings to the tank.

The water inlet and outlet must be positioned correctly, taking into account the physical principles of thermodynamics: fluids and hot air tend to rise (see thermosiphon principle). Therefore, the cold water inlet (from the mains) should be positioned at the bottom and the heated water outlet at the top.

To ensure that the assembly remains secure (particularly when pressure rises due to increased temperature) and that it is properly sealed, it is recommended that it be rigidly fastened. Here, the body of the tank is sandwiched between two pieces of wood and held in place by threaded rods and nuts.

Then position the heating elements around the tank, sticking them directly onto the wall to ensure the heat is distributed as evenly as possible. Secure the thermostat at the top with aluminium tape or heat-resistant silicone.

Finally, in order to minimise heat loss, cover the entire assembly with a double-layer insulating film: aluminium/bubble wrap, which acts as an infrared reflector on the inside, like a survival blanket. Cover as much as possible and remember to leave an area open for the pipes to pass through.

Step 5 - Preparation of the water tank structure

The structure of the balloon will serve as an insulated cell for maintaining temperature and improving heating performance.

Here, a PLA tube and two custom-made wooden covers (with a groove to position the tube) will be used to insulate the balloon and serve as a base for positioning the fasteners, which must be adapted to suit the location where the balloon will be installed.

Position the heating element inside this structure, right in the middle, and fill with insulating material such as wool, hemp or similar.

Step 6 - Electrical connections

Connecting the electrical supply couldn't be easier! Simply connect the heating element directly to the power source (+ to + and - to -). To make cleaning and maintenance easier, we recommend using quick connectors.

Step 7 - Plumbing and water connections

The connection to the other elements of the network and the plumbing are the same as those described in the tutorial: Participatory Science: The mist shower. All the details and possible variations are explained in this tutorial.

Here, for the Biosphere's water heater, the following components were used :

• A plumbing pipe with a valve;
• 3 misters with adjustable jet power (position depending on your use: 1 above the head with medium jet, 1 at upper body level with medium jet, 1 with powerful jet for the hand shower);
• Plastic connection pipes and red plastic taps.
• The choice of connections for the heating core and other elements of the system will allow an easy connection to both the water supply and the misters.

Translated with DeepL.com (free version)

Step 8 - Installation

Installing it as close as possible to the shower will help conserve hot water by minimising losses. It can therefore be installed on a custom-made structure or directly on the wall, as was done for the Biosphere. Here, two wooden ‘brackets’ have been positioned underneath, and the upper part is held in place by a strap attached to the wall.

The structure and fastenings must be strong enough to withstand stress and not pose a risk of falling and injuring someone.

Here is an image showing a complete installation created as part of an experiment (not conducted by Biosphère Urbaine).

1. Water tank
2. Overhead mist sprayer
3. Body-level mist sprayer
4. Rinse shower (with a more powerful jet)
5. River in which soapy water is filtered by bacteria via a biofilter to be re-used in a closed water circuit, known as bioponics.

Step 9 - Tests

Before enjoying hot water and this new washing experience, it is recommended that you test the system and check that it is watertight and that the heating system is working properly. These tests can be carried out as you complete each step, but a final check should be performed.

Water test :

To do this, once the unit is plugged in and connected to the water supply, open the water inlet valve and let the water run through all the pipes. Then check that there are no leaks or water running out.

This step must be performed without electricity to avoid problems with electrical components or electrocution.

Electrical test

If the installation is watertight and you have ensured that there is no risk of leaks, you can connect the system and test the electrical components.

Check the water temperature rise and ensure that there is no overheating that could lead to complications (fire, component melting, etc.).

Once the hot water has reached the desired temperature, take a container and pour the water into it. This will allow you to check the temperature of the water using a thermometer. You can also take a chance and wet your body directly with the water jet.

Maintenance :

For maintenance, remember to clean the water heater thoroughly and check the seals regularly. If in doubt, switch off the electricity.

If everything is in order, enjoy your new shower and take pleasure in seeing your water and electricity bills go down. Your wallet and Mother Nature will thank you.

Step 10 - Use

For instructions on how to use it, particularly in combination with the mist sprayer, please refer to the detailed instructions in the tutoriel.

To sum up :

• Turn on the two medium-jet misters to mist the body (note that the first three seconds are cold).
• Once the body is moistened, turn off the taps (or leave them on) and apply soap.
• Rinse with the powerful jet shower head.
  

How is grey water reused? In the Biosphere, the soap used is a neutral soap, free from chemicals and fragrance, which is ideal for reducing water contamination and, subsequently, environmental contamination. We have installed a biofilter to filter grey water. After analysis by the RITTMO laboratory, the shower water that has passed through the biofilter is suitable for watering our plants. This is why the water is automatically pumped into the apartment's bioponics system.

Notes and references

• References and inspirations:
  • Explanatory video : https://www.instagram.com/p/C-X_HQ7NywH/
  • https://space.stackexchange.com/questions/36066/how-did-skylabs-space-shower-work
  • https://solar.lowtechmagazine.com/2019/10/mist-showers-sustainable-decadence/
• English translation : Quentin Bruyère
• Spanish translation :

Commentaires

This solar electric water heater prototype was developed by :

Water heater : Corentin De Chatelperron and S.M.A.T.

Insulating tube : S.M.A.T. and Frédéric Piro

Mist sprayer installation : Corentin De Chatelperron

This tutorial was written by Anthony Delforge and Caroline Pultz, and published by Quentin Bruyère.

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