ALPES-MARITIMES · SUMMER 2026
A drop falls
on a Côte d’Azur roof.
A drop.
It falls on roof tiles, somewhere between Mougins and the sea.
It took weeks to get here. It will leave again in a few seconds.
In September, Mougins and Valbonne are on heightened alert. Cannes is on alert.
This is not a forecast. It is the order in force as you read these lines.Status as of 30 September 2026
And the drop is already sliding towards the gutter.
Rain on a tiled roof, Côte d’Azur. Illustrative image.
The textThe three tiers
Since 1 June 2026, the whole département has been under a drought watch.
As of 31 July, 83 communes were under restriction.
Watering a lawn is banned there. By day. By night.
Golf courses cut their watering by 60%. Beach showers are closed.
In detail
Here, each person uses an average of 228 litres a day.
In the Nord-Pas-de-Calais: 109.
The difference has a name. Gardens. Pools. Summer.
Sources
Sources: Préfecture des Alpes-Maritimes (alpes-maritimes.gouv.fr), press releases June–September 2026 · Selectra, PACA regional consumption.
AT THE EDGE OF THE GUTTER
Two fates.
And three questions.
On the left, the downpipe. The drop joins a storm drain, then the sea. Lost to your garden.
On the right, a filter, a pipe, a buried tank. The drop stays with you.
The choice looks technical. It is a legal one first.
Three questions decide if your tank is a formality… or a dossier.
It is not the tank that creates the risk. It is the paperwork that was never done.
In detailThree questions
Question 1
Where does the water go?
To the garden, and only to the garden: no declaration. Not before the 2024 reform, nor after.
No declarationQuestion 2
What sits above it?
Nothing — or an inspection hatch: no planning authorisation, whatever the volume. 3,000 litres or 30,000, the Code de l’urbanisme (France’s planning code) makes no distinction.
No declarationQuestion 3
What is connected to it?
A single WC plumbed into the tank, and everything changes. The declaration becomes mandatory.
Declaration requiredThe text
In detailThe hidden defect
Why insist so much on a declaration?
Because in September 2026 a property lawyer described the case of a tank discovered eight years after it was installed.
Sale blocked. The buyer has two years from the discovery to claim a hidden defect (vice caché).
And the water from the shower? It can water the garden too. Since 1 September 2024, it has been written into the rules.
But it is declared to the prefect (the State’s representative in the département), not to the town hall. More on that below.
[[TO CONFIRM: the legal basis for the town-hall declaration after the 2024 order must be validated by the lawyer]]
Sources
Sources: Arrêté du 12 juillet 2024 (base AIDA – INERIS) · CGCT art. R. 2224-19-4 · Code de l’urbanisme art. R. 421-9 à R. 421-12 · Me Reda Kohen, lawyer, analysis of 23 September 2026.
UNDER THE LAWN
The arithmetic
of a roof.
A roof is not measured along its slope. It is measured flat.
A 150 m² tiled roof: 107,000 litres a year at most.
Before the tank: a filter. A mesh of one millimetre, at most.
Inside the tank: darkness. Water kept from light does not turn green.
Concrete or polyethylene? No legal text settles it. The ground does.
There is a second circuit. One for the water you have already used.
In detail3a — The calculation
Rain falls vertically. Only the footprint counts: length × width.
A roof coefficient: 0.9 for tiles or slates, 0.6 for a gravel-topped flat roof, 0.5 for a green roof.
A filter coefficient: 0.9. And the rainfall of the place: 881 millimetres a year in Cannes, according to Météo-France.
An estimate. The site survey does the rest.
The textWhat an installation must have, declared or not
That is the standard: the arrêté du 12 juillet 2024 requires it upstream of storage tanks.
The vents are screened — one millimetre, again — against mosquitoes.
The overflow goes into the ground or the storm drain. Here, never into the sewer.
Between this water and your drinking water: nothing. Not a single connection. And if the mains tops it up: a total-overflow disconnection, with a visible air gap.
And on every tap, a few words: “eau non potable” (non-drinking water).
In detail3c — Concrete or polyethylene
| Concrete | Polyethylene |
|---|---|
| Naturally neutralises the acidity of rain. | No effect on pH. |
| Thermal mass: the water stays cool. | More sensitive to changes in temperature. |
| Up to about 20 m³. | Wide range of volumes. |
| Heavy — a more demanding installation. | Light. Filter, pump and overflow often pre-fitted. |
| Stable, does not crack in frost. | Never cracks in frost. Unaffected by UV and soil pressure. |
Buried, a tank lasts more than twenty-five years. Above ground, ten to fifteen.
And buried, it does not argue with the landscape.
For the Département’s grants, 3,000 litres minimum. For a villa and its garden, the survey sizes it well beyond that.
In detail3d — The second circuit
Showers, baths, washbasins, washing machines: greywater. Never WCs. The kitchen sink, often excluded — too much grease.
Screening. Biological treatment. Membrane filtration. UV. Four stages before storage.
A system that is more complex, more costly and more demanding to maintain than rainwater.
And more tightly regulated by law. That is the next stage of the journey.
Sources
Sources: Technical sheets from CAUE Occitanie, La Maison Saint-Gobain, Test-Achats (sizing, materials) · Arrêté du 12 juillet 2024 (technical requirements) · Règlement CASA aide récupérateur d’eau (1 mm and 3,000 L thresholds) · Eawag, manufacturers’ guides (greywater).
WHAT THE LAW REQUIRES
Two bodies of law look at your tank.
Water law. Planning law.
Water law is concerned with what flows.
Planning law is concerned with what can be seen.
We read the regulations. Not the summaries.
CANNES
The PLU (the local urban plan) caps earthworks at 1.50 m from natural ground level. But it expressly exempts « les constructions souterraines situées intégralement sous le niveau du sol après travaux » (“underground structures lying entirely below ground level after the works” — our translation). A buried tank fits within that sentence.
VALBONNE · Our translation
“The entire territory of the commune is protected as a registered site. Consultation of the ABF [the state architect for heritage sites] is therefore mandatory.”
« L’ensemble du territoire communal est protégé au titre du site inscrit. La consultation de l’ABF est donc obligatoire. »
One rule to remember: it is not the tank that is the problem. It is the grey area.
And a tank declared when required is a tank you can resell.
The text4a — Water law
Since 1 September 2024, a single framework has governed rainwater and greywater at home: décret n° 2024-796 (a government decree) and the arrêté du 12 juillet 2024 (a ministerial order). The 2008 order has been repealed.
Rainwater, for watering or washing outdoors: no procedure.
Greywater, for watering: a declaration to the prefect (the State’s representative in the département). Quality A required.
Greywater, for WCs or a fountain: quality A+.
Then tests, every month, for the first two months. And an owner responsible for the installation, for the long term.
The text4b — Planning law
A fully buried tank creates no floor area. So neither a déclaration préalable (prior declaration) nor a permit. Whatever the volume.
What counts is what shows above ground. A visible plant room of more than 5 m²: déclaration préalable. More than 20 m²: building permit.
And within a perimeter protected by the Architecte des Bâtiments de France (the state architect for heritage sites), the déclaration préalable becomes systematic.
[[TO CONFIRM: application of this rule to a tank with no floor area and no visible footprint]]
In detail4c — Three communes, three texts
CANNES
The same regulations settle the fate of rainwater: infiltration first, then spreading across the plot, and connection to the wastewater network is prohibited (article 4).
Loi Littoral (France’s coastal law): of the three communes, only Cannes is subject to it. It targets the extension of urbanisation — not a buried tank beside an existing villa, in an already built-up neighbourhood.
The Bordeaux administrative court of appeal said as much about a 16 m² pool built against a house: it is not an extension of urbanisation. Soulac-sur-Mer, 23 February 2021. The reasoning holds by analogy. By analogy — not as a guarantee.
Two real exceptions: the 100-metre strip outside urbanised areas, and the espaces remarquables (protected outstanding natural areas) — zones AL and NL. There, there is no debate. We check the plot.
VALBONNE
These are not our words. They are the words of Valbonne’s PLU (the local urban plan) regulations.
The whole commune — not just the bastide. And no “buried = exempt” clause as in Cannes: the national rule applies, with the ABF on top.
Loi Littoral: not applicable. Valbonne is an inland commune.
MOUGINS
In the old village, two listed monuments: the Notre-Dame-de-Vie chapel, 1927, and the Porte Sarrasine, 1942. Each casts a 500-metre perimeter. The historic heart is covered.
For the rest of the commune, we check plot by plot before giving you an answer. We prefer a delay to an approximation.
Loi Littoral: not applicable.
Sources
Sources: Décret n° 2024-796, arrêté du 12 juillet 2024 (base AIDA – INERIS) · ARS PACA · Code de l’urbanisme art. R. 421-9 à R. 421-12 · Règlement PLU de Cannes (updated 2 April 2026), art. 3 · Règlement PLU de Valbonne (updated 2 April 2026) · CAA Bordeaux, 23 févr. 2021, n° 19BX03643 · Base Mérimée (Mougins monuments).
THE GARDEN, UNDER RESTRICTION
The drop comes back up.
The garden stays green.
A 4 × 8 m in-ground pool: 48,000 litres to fill it. About 16 m³ replaced every year.
And while the order stands, the mains tap may no longer water.
The tank, though, holds water that fell on your property.
The text · Our translation
“The measures restricting and suspending water uses do not apply to the use of water drawn directly from reserves built up outside drought periods or from rainwater (reservoirs, rainwater collectors). However, such watering is discouraged during hours of high evaporation (9 am to 7 pm in summer).”
« Les mesures de limitation et de suspension des usages de l’eau ne concernent pas l’utilisation de l’eau prélevée directement dans les réserves constituées hors période de sécheresse ou par l’eau de pluie (retenues, récupérateurs eaux de pluie). Toutefois, ces arrosages sont déconseillés pendant les heures de forte évaporation (9 h à 19 h en été). »
Prefectoral order “Alerte Siagne aval” (alert, lower Siagne basin), signed on 16 July 2026, article 2.
Main residence, for CASA.
A documented tank is a selling point. A forgotten tank is a hidden defect.
A Côte d’Azur garden in summer. Illustrative image.
In detail5a — What a garden drinks
One watering: 15 to 20 litres per square metre.
In the sun, a lawn loses 3 to 6 of those a day to evaporation.
In summer, a garden pushes a household’s consumption up by 20 to 50%.
Discouraged between 9 am and 7 pm, when everything evaporates. Not banned.
What we would rather tell you
What we would rather tell you
At €3.70 per cubic metre — water and sewerage, SICASIL area (the local water authority) [[TO CONFIRM: 2026 SICASIL rate]] — a tank will not make you rich.
107,000 litres a year at most is 107 m³. Less than €400 worth of water. That is not its purpose.
Its purpose: that the olive trees you planted, the lawn you sowed, survive the summer. And the order.
The text5b — Grants
The Communauté d’agglomération Sophia Antipolis (the local inter-municipal authority) adds 10%. Up to €1,000.
In Valbonne and Mougins, yes. In Cannes, no: Cannes belongs to a different inter-municipal authority. Only the Green Deal 06 applies there.
Conditions: a buried or integrated tank, 3,000 litres minimum. One grant per tax household. No purchase before the Département’s notification; CASA also requires installation within two years.
And one condition we would rather tell you about now than at the quote stage:
A second home is not eligible for the CASA top-up. The Département, for its part, accepts it for a rainwater tank. We will tell you at the survey stage, not afterwards.
[[TO CONFIRM: to be confirmed by phone with the Département (08 00 03 70 16) before publication]]
For greywater, we have found no equivalent grant to date. We are telling you that too.
In detail5c — Resale
On the day you sell, what remains is a file.
Quote, technical data sheet, grant certificate, declaration — if one was due.
Sources
Sources: CAUE Occitanie, Selectra, Consoglobe (garden and pool consumption) · SICASIL, 2024 rates · Règlement CASA aide récupérateur d’eau (VF3) · Département 06, Green Deal 06 · Arrêté préfectoral “Alerte Siagne aval”, 16 July 2026 · Me Reda Kohen, 23 Sept. 2026.
BEFORE THE NEXT RAIN
Decide where
the next drop falls.
AquaVillaRiviera is a new firm.
It was born of a team that has tended local gardens and pools since 2006 — Flexi Services.
We will not show you installations we have not yet carried out. We will show you the texts, the calculations, and a method.
- 01
The survey.
The roof, the slope, the plot, the zoning, the commune. We measure, and we read the PLU, before telling you what has to be declared and what does not.
- 02
The quote.
A volume, a material, a price excluding VAT. And the grant you are actually entitled to — main residence or not, Cannes or CASA.
- 03
The installation.
A trench, a tank, the connections, the declarations that are required. And the garden closed up again behind us.
The next drop will fall.
Let it stay with you.