Hydrogeological situation on 1 October 2025
The rainfall at the end of August and September meant that the first recharge episodes were observed in reactive aquifers. The levels in inertial aquifers remained lower than normal. However, the trends started to reverse with 29% of levels rising (compared with just 9% in August).
The situations improved in comparison to August and were generally satisfactory, with levels ranging from moderately low to moderately high. The situation remained worrying in the aquifers in Roussillon, Aude and Southern Corsica, where levels were low to very low.
However, the conditions forecast in October should allow the recharge period to begin in all the aquifers. The trends and any changes in situations will essentially depend on how much rain falls locally and how sensitive the aquifers are to rainfall.
Groundwater situation: a new map and more frequent bulletins
The BRGM groundwater status report, which is eagerly awaited by the public every month, is being revamped. It will now be published twice a month, and the map will have a new colour scheme to make it easier to read.
As of 1 July 2025, the comparative map between the current month and the same month of the previous year will also be reissued with the new colour scheme.
Map of aquifer levels in mainland France on 1 October 2025.
© BRGM
Evolution of the trends observed on piezometers from October 2024 to September 2025.
© BRGM
Trends
This year, the depletion period set in early (February 2025) in the reactive aquifers in a large part of northern France, during the spring in the inertial aquifers in the Artois region and the Paris Basin, and between April and May in the aquifers in the southern part of France and Corsica. In certain local areas, the summer storms reduced the rate at which reactive aquifers were emptying. From the end of August onwards, the first recharge episodes were observed in the reactive aquifers.
This year, the month of September would seem to have marked the transition between the depletion period and the recharge period. The trends started to reverse with 29% of levels rising (compared with just 9% in August). The total rainfall was sufficient to seep deep into the ground and result in recharge episodes.
The levels in inertial aquifers generally remained on a downward trend. This scenario is quite normal in September, since it can take several weeks for rainfall to filter deep down into the ground.
Rising levels were observed locally in the south-western part of the Paris Basin and in the eastern Lyon area, due to heavy rainfall and lower abstraction rates.
Many reactive aquifers in the southern two-thirds and north-east of the country had stable or rising levels in September. The total rainfall at the end of August and in September was sufficient to filter deep into the ground and result in recharge episodes. In addition, the drop in temperatures reduced the amount of water needed by vegetation, meaning more rainfall was able to reach the aquifers.
The depletion of reactive aquifers continued in September, in local areas that had a lack of effective rainfall. This was notably the case in the aquifer in the Armorican Massif, despite certain small recharge episodes, and in certain aquifers in the Aquitaine Basin and along the Roussillon and Languedoc coasts.
Comparison between 1 October 2024 and 1 October 2025
Map of France showing the state of the aquifers on 1 October 2024 (left) and 1 October 2025 (right).
© BRGM
Evolution of the situation observed on piezometers from October 2024 to September 2025.
© BRGM
Aquifer situation
The levels observed during the winter of 2024-2025 were generally satisfactory. The situation then deteriorated progressively from February 2025 in a large part of northern France and from April-May in the south. In August, the levels in the aquifers stabilised, but situations varied depending on the areas.
In September 2025, levels were generally satisfactory, ranging from moderately low to moderately high. The situation improved compared with August: the levels recorded at 31% of the observation points were below monthly averages, 23% were comparable with monthly norms and 46% were above average (compared with 38%, 29% and 33% in August, respectively).
The situation was much more satisfactory in September 2024: 73% of levels were above monthly norms, due to the abundant recharge in 2023-2024, boosted by the rain that fell in spring 2024. In 2025, the only aquifers whose situation was better than in 2024 were the highly inertial aquifers in the Beauce and Sundgau regions (southern Alsace) and certain aquifers along the Mediterranean coast.
Inertial aquifers
The state of the inertial aquifers hardly changed between August and September 2025. The levels remained satisfactory, ranging from moderately low to moderately high.
In the Artois and Paris Basin, the situation observed was worse in the less inertial marl chalk aquifers in the coastal area of the Artois and the Champagne region, which were more affected by the lack of rainfall from February onwards. On the other hand, the situation was particularly satisfactory in the highly inertial aquifer in the Beauce region. Very high levels were observed in the north-western section of the area.
The levels of the aquifers in the Sundgau (southern Alsace) and the Rhône-Saône corridor were generally in line with monthly norms. However, the situations varied locally, with levels ranging from low to high. For example, the levels in the fluvio-glacial alluvial aquifer in the eastern Lyon area were high, due to the decrease in abstractions and the start of the recharge period.
Reactive aquifers
The heavy rainfall at the end of August and September had a significant effect on many reactive aquifers. The impact of rainfall was particularly notable in the aquifers in the Massif Central, whose situation improved significantly. Finally, the situation remained stable in the aquifers in the Armorican Massif, the southern Massif Central, the Mediterranean and Corsica.
In many areas, the reactive aquifers returned to satisfactory levels, essentially ranging from moderately low to moderately high.
High levels were observed in the aquifers of the lower Rhône, the western Massif Central and the Côte-des-Bars. In certain local areas, the observation points even had very high levels. The recharge was particularly abundant in these areas in September, leading to a considerable improvement in the state of the aquifers.
The situation remained worrying in the aquifers in Roussillon and Aude, where levels were low to very low. The aquifers in the extreme south of Corsica (Alta Rocca, Balagne and Fium'Orbu) were also in a very poor state in terms of their levels. These aquifers need to be closely monitored over the coming weeks. In addition, there were also a few low to very-low levels observed in the aquifers in the Jurassic limestone formations of the Lorraine and Berry regions, as well as in the aquifers in the volcanic formations of the Massif Central and the basement formations of the Limousin region.
Aquifers with surplus water
Several aquifers had very high levels, when compared with those recorded for September in previous years:
- The high to very high levels observed in the Beauce aquifer can be explained by its very inertial nature. Indeed, this aquifer is still reaping the positive effects of the surplus recharges in 2023-2024 and 2024-2025;
- The recharge episodes in September considerably improved the state of the aquifers in the Jurassic limestone formations of the Côte-des-Bars and in the basement formations of the western Massif Central;
- The alluvial aquifers of the lower Rhône and its main tributaries benefited from the rain that fell in recent weeks.
Aquifers with low water levels
The situation was unfavourable in several aquifers, with low to very low levels compared to those recorded for September in previous years:
- The levels in the Roussillon multilayer aquifer and in the aquifers of the karst limestone formations of the Corbières Massif remained low to very low;
- Due to a continuing lack of rainfall, the alluvial aquifer in the Aude remained at a low level;
- The aquifers in the far south of Corsica were affected by the lack of rainfall over the last few months.
Key figures
-
29.00%of levels increased
-
46.00%of levels were above monthly averages
-
29.00%of levels were below monthly averages
Forecasts
The Météo-France seasonal forecasts for October, November and December 2025 predict higher temperatures across the whole of France. No clear scenario has been established concerning rainfall.
The beginning of autumn is a pivotal period, between the end of the summer depletion (falling levels) and the beginning of the winter recharge (rising levels). The reversal of trends observed in August-September suggests the recharge period will start early this year. However, if the current trend of rising levels is to continue, there must be a sufficient amount of rainfall that infiltrates deep into the ground, and this will depend on two factors: the total rainfall in the coming weeks and the time at which the vegetation enters its dormant period. As long as the vegetation remains active, due to high temperatures, the recharge episodes will be limited.
Inertial aquifers
As regards the inertial aquifers in the Artois and Paris Basin, effective rainfall has been insufficient to reverse the trends. The recharge period is not expected to begin until the vegetation has become dormant and significant rainfall has occurred, i.e. from the end of October onwards.
The Sundgau region and the Rhône-Saône corridor have received plenty of rainfall recently, and the low-water period in these aquifers is likely to occur as of October in the least inertial aquifers.
Overall, the situation in the inertial aquifers should remain stable and relatively satisfactory over the coming weeks. During the winter, their situation will evolve slowly, depending on the recharge episodes.
Reactive aquifers
The conditions forecast should allow the recharge period to begin in all the aquifers during the month of October. In the areas that have received a lot of rain recently, the effects should be quickly visible. However, the depletion of the aquifers could resume, if the effective rainfall is insufficient.
During the autumn and winter, any changes in the state of the reactive aquifers will essentially depend on the total amount of rainfall. The situations could change rapidly, in the space of just a few weeks. The current situation does not allow us to predict what will happen in the coming months and say whether there will be either a period of drought or flooding due to rising groundwater.
A close eye needs to be kept on the aquifers in which low to very-low levels were observed in September (Roussillon, Aude and southern Corsica). The current state of these aquifers is extremely worrying and the 2025 low-water point is expected to be very severe. The 2024-2025 recharge period will need to be monitored very closely.
Press contact
State of groundwater: monitoring by BRGM
Groundwater is a widely used resource: in metropolitan France, it accounts for nearly two-thirds of drinking water consumption and more than one-third of agricultural water consumption. It is also widely used in the industrial sector. Groundwater tables depend on cyclical recharges.
BRGM monitors groundwater levels and quality in mainland France. Discover the actions carried out by the French geological survey and the resources and databases available on groundwater in France.
Aquifer recharge: 3 questions to provide a better understanding of the process
How do aquifers fill up and how do they empty?
Groundwater levels vary throughout the year, from high levels in winter (when vegetation does not absorb rainwater) to low levels in summer (the traditional depletion period).
The fate of rainfall varies greatly depending on the time of year and the condition of the ground surface on which it falls. Usually, the groundwater-recharge period takes place from early autumn (September-October) to early spring (March-April), a six-month period during which vegetation is dormant (with low evapotranspiration) and rainfall is generally more abundant. If the winter is dry, groundwater recharge is very low.
From spring through summer, rising temperatures coupled with the regrowth of vegetation and thus increased evapotranspiration, limit the infiltration of rainfall into aquifers. Between May and October, unless there are exceptional rainfall episodes, aquifer depletion usually continues and levels will keep decreasing until the autumn.
Why do some aquifers recharge faster than others?
Groundwater flows at different rates depending on the porosity (percentage of gaps/cracks in the rock) and permeability (capacity to allow water to circulate, i.e. interconnectivity between these gaps/cracks) of the aquifers. The larger the gaps and the more interconnected they are, the faster the water will flow, for both refilling and depletion.
It takes a given volume of water different periods of time to travel the same distance, depending on the kind of rock formation:
- a few years in a porous formation,
- a few months in a cracked formation,
- and a few days, or even a few hours, in a karst formation.
Inertial and reactive aquifers: what are they?
The impact of the winter recharge varies according to the cyclic nature of the aquifer, i.e., its reactivity to rainfall infiltration.
We refer to aquifers that are:
- reactive (when they are composed of sand, gravel, karst limestone or weathered granite formations). These aquifers are characterised by their rapid reaction times: they can recharge during heavy summer rainfall, but are also highly sensitive to drought. Their levels can therefore vary very quickly over the course of the same season.
- inertial (when composed of chalk, non-karst limestone, sandstone formations). Their reaction times are slow. They can have multi-annual cycles, meaning that they require a long period to recharge or empty.
Cyclicity of aquifers in mainland France.
© BRGM
Map drawn up by BRGM on 6 October 2025, based on data acquired up to 30 September 2025.
Data source: ADES (ades.eaufrance.fr) / Hydroportail (hydro.eaufrance.fr) / Background map © IGN. Data producers and contributors: APRONA, BRGM, Conseil Départemental de la Vendée, Conseil Départemental des Landes, Conseil Départemental du Lot, EPTB Vistre Vistrenque, Parc Naturel Régional des Grandes Causses, Syndicat Mixte d’Etudes et de Travaux de l’Astien (SMETA), Syndicat Mixte pour la protection et la gestion des nappes souterraines de la plaine du Roussillon (SMNPR).
This map shows the global indicators reflecting the average fluctuations of the aquifers. They are based on point indicators collected at groundwater monitoring points (by means of piezometers).
The "Aquifer levels" indicator compares the current month’s figures with those of the same months in the entire record, i.e. at least 15 years of data and sometimes up to as much as 100 years of data. It is divided into 7 classes, from the lowest level (in red) to the highest (in dark blue).
The grey areas correspond to areas without unconfined aquifers, i.e. with an impermeable or semi-permeable layer above the aquifer, and/or sectors with a very low density of measuring points. This last case primarily concerns mountainous areas with small, heterogeneous aquifers.
The "Evolution of levels" indicator reflects the variation of the water level of the past month compared to the two previous months (stable, increasing or decreasing).
These global indicators reflect general situations and trends and do not take into account possible local disparities.