Fosse Septiques (Septic Tanks) in France

Buying a French property is often the start of many a new experience. Receiving an invitation from the neighbours for an ‘apero,’ strolling to the village boulangerie for a freshly baked baguette or simply exploring the local market, these are all often ‘firsts’ for new property owners. Becoming the owner of a septic tank or une fosse septique for the first time, is a slightly more mundane experience but one that is often an integral part of owning a French property.

Unlike the UK, where the vast majority of homes are connected to the main sewage system, many French properties have stand alone systems - l’assainissement non collectif - for waste disposal. Over the last few years, France has been upgrading many town and village installations and connecting households to mains drainage, which is known as tout a l’egout. Communes with over 2000 inhabitants are expected to provide a treatment station and if there is no existing system of connection in place, to provide one. In certain circumstances, communes may be allowed to opt out of this responsibility and retain stand alone systems. If this happens, the commune is then responsible for checking that all the waste systems comply with current regulations.

Given that many communes have far fewer than 2000 inhabitants and as many French properties are simply too isolated to make connection to a main system practical, it seems that the septic tank or la fosse as it is commonly known, is here to stay. Years ago the septic tank was designed just to tackle sewage waste from any toilets in the house. Waste ‘grey’ water, i.e. water from sinks, showers and washbasins was directed to a soak away in the ground or very often, just left to run off into the nearest ditch. In the days before most households had washing machines and dishwashers and when bathing was a weekly affair, this might just about have worked. These days there is a clear need to prevent untreated waste water seeping into the natural environment so the standard now is for a fosse tous eaux where the fosse deals with all the waste water from the property.

With this in mind, the local professional body responsible for waste management systems will be inspecting septic tanks throughout France before 2012 to ensure that the installation is not polluting the environment. These bodies vary from region to region - ask at your local Mairie for details but one of the most widely known is the SPANC or Service Public d’Assainissement. Unless your system has been recently installed, it is unlikely to comply and the SPANC will advise you on how to upgrade it to current standards. They will need access to any inspection covers for both the tank itself and any filter bed. Older septic tanks may be totally buried and this can make them almost impossible to find. With no trace of covers let alone the tank itself, some detective work is called for. Nettles often grow well over the soak away area and this can be a good starting point in your hunt for la fosse. You could also try asking the neighbours or the local company which empties septic tanks. Very often, especially in rural areas there is just one company which deals with this and they tend to know the whereabouts of each fosse. If all else fails, you will need to start digging! The SPANC tend to be very helpful and inspectors will often go out of their way to provide you with pointers that will enable your system to comply. However, if they consider the system to be an environmental or health risk, they will insist that you carry out the necessary work detailed in their report to bring the fosse up to standard. You will be allowed up to four years to undertake the work and some financial assistance may be available from the DDASS - le Direction Departmentale des Affaires Sanitaires et Sociales.

If you have bought a property with no septic tank at all, you will need to start by visiting the Mairie. They will be able to tell you if there are any plans to install mains drainage and if so, when this is scheduled to happen. If not and you need to install a septic tank, they will give you a form to complete. This is the ‘Demande d’Installation d’Assainissement Non Collectif’ and unless you have applied for permission previously and understand exactly what is required, it is best to ask for a meeting with the professional body responsible locally for managing waste systems. They will advise you as to exactly what type of system you require. Any new installation will require a soil survey to determine the type of filtration system required and the SPANC or their equivalent will be able to do this. You will need to tell them how many bedrooms the property will have as this will determine the tank size. The eventual solution they recommend will depend on the nature of the soil, its permeability, the slope of the land, the presence of bedrock and nearby wells. Depending on the proposed location of the septic tank, you may also need to install a pump to facilitate water flow from the fosse to the soak away. A grease trap - bac a graisse - will need be installed and all of these factors will affect the eventual cost of the system. Once you have this information, you can approach septic tank installing companies for quotes. It is always worth asking the technician from the SPANC for a contact. They will usually recommend an installer who is efficient and will do the work to the required standard. The installer will be able to help you draw up all necessary plans, showing the position of the tank, grease traps, filtration system, inspection covers and so on that are required by the Mairie for the completed application

So how does a septic tank actually work? There are basically two phases in a septic tank installation, the pre-treatment and the treatment stage. During the pre-treatment stage the tank stocks the water and sewage coming from the house and allows the separation of matter to occur. Floating matter, oils and grease forms a scum like layer at the top whilst the solid matter settles at the bottom of the tank. Biological action within the tank will cause liquefaction and it also produces gases such as methane and hydrogen sulphide. As well as smelling vile, these gases can be toxic in concentrated amounts which is why it is necessary to install a ventilation pipe as part of the system. This pipe will usually run up the gable end or appear through the roof and be placed as far away as possible from openings such as windows or roof windows.

The treatment stage involves purifying the pre-treated water and then allowing it to disperse into the environment. This is carried out by the microorganisms which develop within the system. They consume the organic matter in the waste water in order to live and develop and once the waste water has passed through the treatment stage, it can simply soak away into the ground. The most common method for this final treatment stage is shallow drainage ditches containing perforated pipes laid within a thin layer of gravel, wrapped in geo-textile and then a thin layer of soil. Grass can be sown but you will not be able to plant trees or large shrubs. Some soil types will require the installation of a sand filter or filtre a sable. These work on the same principle but require the addition of layer of sand plus an extra layer of gravel. Sand filters are more expensive to install so it is always good news when the soil technician tells you that you don’t need one!

If the system has been correctly installed, the size of the tank is right for the house and the fosse is emptied at regular intervals, living with une fosse septique should pose no problem. Make sure that nothing is flushed down that cannot be broken down by microorganisms and if you rent out your property or have lots of visitors, a ‘warning’ notice is a good idea. If the property is a holiday home, you may want to consider a microorganism starter kit. These reactivate the breakdown process after a period of inactivity, as does live yoghurt. They are widely available in supermarkets and DIY stores and many people in permanent residence also use them to ensure that the micro-bacterial process is working at full capacity. Most cleaning products are marked to indicate whether they are fosse friendly and ideally, bleach based substances should be avoided.

Useful vocab:

Grease trap - bac a graisse

Mains drainage - tout a l’egout

Septic tank - la fosse septique

Sand filter - filtre a sable

Connection to mains drainage - raccordement au reseau du tout a l’egout

Your septic tank will need to be emptied according to use. Obviously a couple in a holiday home will generate far less waste than a family in full time residence but a general rule of thumb is:

Clean the grease trap every six to twelve months and have the tank emptied every three years.

Installing a waste system is a major undertaking and if possible, it is wise to do this at the start of renovation works to give the ground time to recover.

© Catharine Higginson

Hi Folks,

We are just in the process of buying our first french property and are having to do the usual upgrade to the septic tank. We have a garden but it isn't huge and are wondering what would be the best system to go for. It will initially be a holiday home but we hope to move over permanently in five years. I've been reading all the posts on hear and have seen some comments about the biorock sysytem suffering from frequent failure. One poster said they had installed the Klaro East system. Can anybody give me an advice or feedback on these systems? Many thanks.


Just seen your post Nina. There is an interesting page on the problems with reed beds on We looked at them, but they might not be as 'eco' as they seem?

Can anyone tell me if this is true? I have been told that for holiday homes in France, SPANC will only allow non-electric micro-stations like Filterpod? I was looking at Klargester, but am told that they are not allowed unless you actually live in the house full time?

I can't find many non electric ones and they are all very expensive.

We are renovating a property in the department Lot of France and need to install a Sewage System as we are off mains sewage.

We have shortlisted to the following 3:
1. Compact Filter System/ Les Filtres compacts
2. Reed Bed/ Les Filtres plants
3. Micro-Station/Les microstations a culture fixee/libres
Ideally we would like to use the Reed bed system due to environmental reasons but are worried it will come with high costs for installation/large footprint and general complications of setting it up.
The available area to us is around 5x5 metres and we don't really want to lose any more garden than that.
Does anyone have any feedback/info on the 3 system options above and also on products/companies used?
Look forward to hearing some feedback!

I live in the Pays Basque on top of a small mountain in the Pyrenees. We bought the house in 2005 and the previous owners told us we would never have to empty the fosse. And we haven't. We have not been inspected by SPANC but are about to sell the house. There are no inspection covers and we have no idea where the fosse is except that it sits somewhere down a steep slope. At the bottom of the slope is a massive field (4 hectares). There are absolutely no clues as to where it is. So what do we do? It is really tricky digging holes in solid rock. What happens if no one can find it?

A very interesting article James - thanks.Luckily when I moved into my ancient house, the previous owners had renovated the house, and installed a brand new septic tank, which complies with all regulations. Last year I had it emptied and all the pipes correctly cleaned etc.

However - a word of warning - a couple of years ago a French neighbour a couple of doors away had a local farmer arrived with a tractor connected to a bowser, who pumped out the neighbour's fosse, and merrily went on his way. This eventually was pumped onto some fields. Some days later the neighbour came to me to offer the farmer's services and told me that I would only pay him 50 euros for his service. I politely declined.

This procedure is totally illegal, and if discovered the owner of the house, and the farmer will be prosecuted with an enormous fine.

I just thought I would mention this as perhaps some folk are not aware of this.

We have a microstation, no need for any filter beds, no sand beds. Just one installation with clean water coming out of it. So much easier, land doesn't get contaminated.

I just had Spanc round to tell me I need to connect to the mains. The guy was friendly enough but when I asked about financial aid from the DASS he laughed. "There is no aid...." I am looking at about €10K for a pump to be installed.

We had a really old septic system which was struggling and smelling, and had never been designed for our house once extended for more bedrooms and super-duper kitchen etc so last year we replaced it with a microstation (Klaro Easy) which has been perfect so far.

It was not on the list from SPANC (they had the smaller version, but not the 5-12 person size we installed) but we found out that it you can install what you like and it is up to SPANC or the Mairie to prove that the system does not conform in terms of polluting ground water. This system essentially goes through two large tanks which work biologically to break down the waste, producing pure, clear water which goes to our existing drainage/gutter water ditch (and no, I have not tried drinking it to make sure it's pure!!).

So far, so good (though I'm touching wood as I say this!). Does not need to be emptied, apparently, as everything is broken down -- apart from the bac de graisse which is then cleared once or twice a year.

Incidentally, when it was first installed it only served one bathroom and the laundry, and we connected the kitchen sinks and dishwashers about 6 weeks later, once more pipes were diverted. In the meantime we checked the bac de graisse and it was astonishing how much white grease had come off bodies and laundry in just that time!!

It was just our luck to find out later than if we had picked one of the 'approved' systems we would have had a 40% subsidy, which is apparently the case for all systems installed now and in the next year or so -- my understanding is that this applies to SPANC-approved systems throughout France, so check with your Mairie.


Hi Sheila

Yes I heard about that one and I find it unsettling, an earlier story really shook me up although I know no-one involved.

We all have to go to meet our maker sometime but I think its only natural we also are sensitive to the way someone goes.

I will be glad when authorities everywhere have hooked us all up to the pipe. The system I have on my campsite is actually based on the same components and principles as used by the authorities in larger treatment plants (I have two diffusers they have hundreds) - the main difference is that they can test daily to make sure that liquids going back into the environment are "clean" - they can deal with safety and just generally do a better and more efficient job.

I find it ridiculous that so much of this is left in the hands of the layman. As far as I can make out many authorities dont really want to deal with this because the costs are considerable but the benefits are not visible the tax paying voter does not get won over by initiatives to deal with systems that look to the casual observer as if they are working perfectly fine.

I think I am developing Obcessive Compulsive on this issue. We have seven steel manhole covers and whenever I lift them for inspection I often have to come back ten minutes later to really really make sure I have them down firmly in place. Actually its not Obcessive at all - I run a public facility!


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Have to interject on the Biorock unit, there has been a high failure rate with the square design collapsing, ask around in the UK - also the cost of replacing the internal matting is unwelcome, and the treated water ends up 1.2m down which is a problem unless you live on the side of a hill - you need a pump to get it up into the soakaway and that negates their whole "no electric" claims right there . . .

Very good warning about safety Jon. A tragic septic tank accident last September claimed the lives of a father and two of his sons.

Hi again.

Safety! When I say "inspect" I would suggest that no-one in their right mind would actually climb into a septic tank even if it has been evacuated and cleaned - thats a job for a pro with knowledge and breathing apparatus.

What I was alluding to is that there is even a risk getting down on all fours and sticking your head down to take a look. The safer way is to lie down so that if you were overcome you would not fall in and also to always have someone else there with you. I have no choice but to perform regular inspections myself (campsite system) but I never do it alone, I make sure my companion understands the risks and I try to breathe in as little as I can etc.


Hi again

I hope most can read past my typos and inconsistent spelling - sorry about those.

The one that needs re-typing is...

2. The bacteria will simply work aerobically if there is sufficient oxygen to do so and anaerobically so any viable solution for aerobic action has to physically get more oxygen into the system.

it should say that "and they will work an-aerobically if there is not sufficient oxygen".....

Incidentally the required bacteria are already in the poo - isnt nature wonderful !! Its not so much a matter of adding new bacteria but rather giving the ones already there ideal conditions to breed and do their stuff. The bacteria consume organic matter considerably faster when they are working aerobically, I forget but I think the touted figure is ten times faster but dont quote me.

Since I added air pumps and diffusers the bottom of our secondary tank is clear of sludge - the little marvels got so good at eating the "incoming" that they stared dealing with the legacy stuff as well. Do be careful to protect any drainfields first (filters) as the diffusers do churn up the liquid and can result in more solids floating where they should not unless simple filters are used.

We have opted for something completely different for the house we are renovating! Composting toilets and reed bed purification for grey water. And it has been approved, the 2 reed beds will have different plants growing in it so will be a feature to the garden as the water makes it`s way between them and finish in the mere which is already there. Then the water will be used for watering the garden.



Safety First ....

I am a campsite owner (not in France) and our toilets run on a septic system, same principle as a domestic just a lot bigger. I have had to work long and hard on the system in recent years - professionals are not always reliable sources of information and I felt I need to learn as much as I could myself - there are all sorts of claims and counter claims by folks selling solutions and unless you take some interest it can be hard to sort the wheat from the chaff.

One apsect I would like to underline is safety, people including children have died as a result of failiure of concrete structures or manhole covers - the gases in a septic tank will knock the victim out very quickly. It is certainly true that road accidents account for more deaths but perhaps an accident with a septic tank is such a nasty idea I feel motivated to underline the risks. Do not inspect a tank alone and be very wary of getting down on all fours or any other action that gets your nose close to the gases. Be aware that the concrete can be degraded by the chemicals found in a septic tank - this year I am replacing several concrete wells ( not the main tanks but rather smaller wells which are part of the soakaway system ) - the concrete is showing early signs of degrading due to the harsh chemical environment, the inner surface is begining to crumble. Interestingly the concrete is untouched beneath the "water line" so I suspect the chemical action is most agressive in the upper regions that contain gas rather than the lower regions that contain liquid.

Soakaways do degrade over time, same for septic tanks - basically the bacteria that decompose the organic matter can work aerobically or an-aerobically - the latter produces an odious black slimey matt that is unfortunately a barrier to water which in extreme cases can lead to failure and smelly liquid coming up to the surface.

I recently fitted an air pump and defuser system to our septic system - domestic scale systems can cost a few hundred euros. The benefit is that the foul and evil smells migrate to what might be called farm yard smells. The same bacteria that worked an-aerobically now work aerobically - they produce less toxic by products and the matt that can block systems is actually eaten by the bacteria (as long as there is sufficient oxygen).

Fitting an air pump and diffuser has made our system much more pleasent to work with, although there are still smells I feel it is intrinsically safer, healthier and less evil - there are bad smells and there are bad smells and an-aerobic by products really do smell like you could catch something really terrible.

A good book on most principles but with precious little detail on aerobic systems is

"The Septic System Owners Manual" - LLoyd Kahn.

In general the Americans are very good sources of information since a great deal of rural America is not on the pipeline.

For advice on air pumps and diffusers try

John Edgar

Hydra International Ltd.

Cerberian House, Carters Lane, Kiln Farm, Milton Keynes MK11 3ER, UK

Tel: +44 1908-265889 Fax: +44 1908-262097

I found him to be very helpful but please bear in mind his angle of interest is air pumps and diffusers and aerobic systems - try Google to find the company websites although they have more than one.

There are a lot of "snake oil" potions out there like bacteria packs to rejeuvinate the bacteria in your tank but be aware...

1. Its the same bacteria that work aerobically or an-aerobically - snake oil solutions claiming that a sachet of XYZ will replace bad bacteria with good ones are dubious. Powders cannot introduce anything but a boost and cannot deliver oxygen over a long period of time.

2. The bacteria will simply work aerobically if there is sufficient oxygen to do so and anaerobically so any viable solution for aerobic action has to physically get more oxygen into the system.

There is a new technology on the block I have heard some good things about it.

I have no idea if any of the above solutions would be acceptable to the French authorities so please check first.

Simple Maintenance:

If you have a drainfield make sure organic solids cannot enter - solutions involve simpe traps and also T sections which draw liquid from 10cm or so beneath the water line. Most of the solids in a septic float or sink so drawing from below the water line tends to deliver cleaner liquid.

Dont pure oils or fats down, the bacteria dont like it much although some well respected authorties say this may not be as bad as others make out.

Be wary of introducing strong bleaches or cleaning chemicals that can kill off bacteria.

Inspect the system once a year or more if you feel it is required and if you have a drainfield then make sure your system is regularly pumpes so that the sludge at the bottom does not find its way into the drainfield pipes. ( the terms drainfield and soakaway are interchangeable ). Some septic systems run for years without attention but often the difference between hefty bills and a sustainable system is just a little knowledge and occassional inspections.

Kind regards


There are more than 36000 mairies in France, and whilst your article is better than 95% of the ones out there, it misses out on a whole section of the regulations and mentions "sand filters" which are now frankly rare as an option. To bear in mind is that whilst there is a set of "rules" - they are very much open to interpretation - so it's actually impossible to double guess what your obligations will really be until you test opinion down there - with lots of smiling even if through gritted teeth!

If your unit fails or you simply need a new one, basically the first port of call is your Mairie, they will advise what their preferred next step is, the "game" being usually "pass the buck" - ie. "get a soil test"

What most people don't tell you is that there is no obligation whatsoever on having this done by an etude or paying 400-600 euros for the priviledge. Nor will an etude or the Mairie take any responsibility should the new system subsequently fail, so what advantage does it give you? Considering also that many suggest using a system you wouldn't really want to buy, for reason's unknown! For instructions on doing your own soakaway test see

The regulations split between upto 20eh and above 20eh - with above 20eh generally being much simpler to put in place.

The cheapest option, and often preferred option with interest free loans available to cover the cost backed by the French government is a septic tank. Whether you can install one will depend on your soil type and topography - which is where the soil report comes in. To remember is that many sellers will try to get you to sign up for a mini wastewater treatment plant - but if your land is considered big enough, you will still have to install a soakaway just the same - turning it into an expensive fosse!

More and more people are realising that to have a high performing compliant system at the lowest price and suitable for holiday homes, it's worth paying a little more for an improved septic, ( Biofosse ) , which reduces odours, improves performance and protects the soakaway - which is the usual first point of failure in any system. Purchase and installation should be possible under 4000ht by a company or 2600ht if DIY.

If you have limited land, you should be able to get permission to install a micro station d’épuration, with an outflow to a watercourse or ditch, watch out for servicing costs, and models known to block up (fixed bed) as well as avoiding Bouees active, or Impeller types (trust me here). Also if you choose one deemed unsuitable for intermittent use, at the time of selling you have effectively restricted your potential market, so read small print carefully.

And Rosie, yes, get it emptied 85%, clean all filters, and refill immediately with clean water and a few sachets of Eparcyl or similar. Ensure you use a company agree, and keep the paperwork - emptying will be compulsary every 4 years very shortly.

Any other questions, please feel happy to contact me.

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My eyes water at the thought of doing all that again. The fosse system was just one of the didn't-see-THAT-coming aspects of creating this place. We had SPANC (LOVE that name!!) here working with us from day-1. They basically designed the system for us, based on all the surveys and tests they carried out and the number of bathrooms we had planned (14!). We have two 6000 litre fosse tanks, a couple of specialist pumps (1000 euros each!) three peat filter tanks (instead of sand filters), each the size of a small car, and 150 metres of drainage pipes, together with all the grey pipes that connect it all together and electronic controls and alarms. Mr Bourdet (the village JCB man) was here for days digging it all in (there was about 40 tons of gravel involved as well), and at one point it looked like the Somme out there. Initially we were going to buy half an acre from next door for the drainage field but that was before we found out that French agricultural land is SO sacrosanct that you cannot even bury pipes in it. That's when we had to "lose" a couple of big pine trees.

Having lived with septic systems all my life and owned numerous homes with them, best advice is to put a microbial starter down the toilet every month. Everyday cleaners wreck havoc on these systems, even if they say they are safe. (Rid-x is great)