In a student residence, water is included in the service charges and nobody sees what a shower costs. The Molleaumètre displays it in real time, shower by shower, and cuts it by 23% less hot water per shower on average: a result measured in the Relais d'Italie student residence with Hénéo (RIVP group), over 3,140 showers, with no building work and nothing asked of residents.
Because water is included in the flat-rate charges, residents change every year and the shower is the largest single use of hot water in a home. Hot water weighs twice: the water, plus the energy that heats it.
Water is usually included in the flat-rate charges of a student home. Residents never receive a water bill and have no idea whether their shower uses 30 or 80 litres. In the pilot residence, nearly one shower in two exceeded 40 litres before the display.
A student residence largely renews itself at every start of term. Awareness campaigns have to be redone every year; a cue installed in the shower stays in place and speaks to the newcomer from day one.
Every litre of shower water costs the water and the energy that heats it, about 0.03 kWh per litre. With collective water heaters, hot water is one of a residence's largest charge items, and one of the few that can be cut without building work.
The Molleau pilot took place in a student residence: Relais d'Italie, in Paris, managed by Hénéo (RIVP group). 28 homes equipped, 3,140 showers analysed from November 2025 to June 2026, a two-phase protocol: a silent measurement to establish the baseline, then activation of the light ring. Same showers, same residents: only the visibility changed. The average shower went from 45 to 34.7 litres, the share of showers above 40 litres from 48% to 33%, and the residence's main meter fell by 15.5%.
Read the full protocol and results →
The Molleaumètre is a connected water meter that screws between the mixer tap and the hose of every shower. It replaces neither the shower head nor the hose and does not touch the flow rate. No work on the water risers, no sub-meters, nothing asked of residents.
Between the mixer tap and the hose, with no tools and no water shut-off, during usual maintenance slots or at check-in inspections. The device is powered by the water flow: no battery, no socket.
Green, amber, red: residents see their litres during the shower. The optional app adds challenges between residents, eco-tips and points, a format that works well with a young audience. No guilt-inducing message, no change to the flow.
Anonymised data sent automatically: before and after comparison by home and by residence, distribution of showers by band, conversion into euros and tCO₂e, exports for CSR reports and label applications.
About 770 m³ of hot water and €8,400 a year, for a 200-home residence at one shower a day. Projection based on the volume measured during the pilot's baseline phase (45 L per shower) and the measured rate of 23% less hot water per shower; the app's challenges add to this minimum.
| Per year | Projection · −23% hot water per shower |
|---|---|
| Hot water saved | ≈ 770 m³10.6 L per shower |
| Savings (water + heating) | ≈ €8,400 *≈ €42 per home |
| CO₂ avoided | ≈ 4.8 t≈ 24,800 kWh of heating avoided |
* Indicative estimate calculated with the assumptions used in the Molleau calculator: water and sewerage at €4.69/m³ (French national average, SISPEA 2025), heating from 15 °C to 41 °C (around 0.030 kWh/L), electricity at €0.1940/kWh (French regulated tariff, June 2026), CO₂ at roughly 0.06 kg/kWh (French electricity mix) plus 0.30 kg/m³ (treatment and distribution). Several occupants per home, communal gas cylinders, local tariffs: every parameter can be adjusted in the calculator. Method: 0.0321 kWh per litre of hot water (38 °C from 15 °C, network losses 1.2), heat network emission factor 0.183 kgCO₂/kWh, water and sewerage 0.35 kgCO₂/m³, ADEME Base Carbone 2025. Water and sewerage €4.69/m³ (SISPEA 2025), electricity €0.1940/kWh (French regulated tariff, June 2026).
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By making the shower visible. The Molleaumètre, a connected water meter with a light ring, screws between the mixer tap and the hose in every home, with no tools or plumbing. In the Relais d'Italie student residence (Hénéo, RIVP group), it cut hot water consumption by 23% per shower on average, up to 61% among the heaviest users.
Because water is almost always included in a flat-rate service charge: residents see neither their consumption nor its cost, and no bill ever reminds them. In the pilot residence, nearly one shower in two exceeded 40 litres before the display; that share fell to one in three afterwards.
Yes. At the six-month review of the Hénéo pilot, median satisfaction is 5 out of 5 and every respondent recommends the device. 83% of residents report increased awareness. Nothing is asked of them, data are anonymised and the app with its challenges remains optional.
That is its advantage over poster campaigns: the cue is in the shower, not in the occupants' memory. Every newcomer sees the ring from their first shower, with no training or reminder from the manager.
A dashboard by residence and by home: number of showers, average volume, distribution by band, savings in litres, euros and CO₂, exports for CSR reports. No personal data is displayed.
The Molleaumètre is offered as a subscription, about €6 excl. VAT per month per device, with a set-up fee at installation. The subscription includes the installed device, the resident app and the manager dashboard. Ask for a study for your residence.
Thirty minutes to estimate the savings potential of your student residence, from the number of homes and your water tariff.