Explainer: the rules around septic tanks in rural France

‘Fosses septiques’ are an unavoidable part of life for one in five French residents

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People moving to the countryside can be surprised that many houses are not connected to a sewerage system, which means none of their familiar flush-and-forget toilets and drains.

It is still not uncommon to find houses with very basic, or no, sewerage systems in rural areas of France, especially those at the lower end of the price range.

Rules have become stricter over the years, and from 2020 if you have an occupied house, you have to have an approved sewerage system.

Read more: How do we connect our French holiday home to public drainage?

Different sewerage options in rural France

Where the commune has a collective system that gathers waste water and treats it, it is now obligatory to connect your house to it within two years of buying the property if you are in the zonage d’assainissement.

These are usually in the main village centre but can also extend to hamlets in the commune. They relate to the home’s proximity to a main sewer pipe.

If the commune does not have a collective system, individual systems will have to be fitted – usually a septic tank.

Alternatives include building a micro sewerage purification plant. Using reed beds for final purification is popular.

Official estimates reckon that up to a fifth of the population live in houses with individual sewerage systems.

This might partly be explained by the fact that rural people often oppose having sewerage plants built near them for environmental reasons or due to smells.

Each commune, or grouping of communes, now has its own service public d’assainissement non collectif, or SPANC, which regulates individual systems.

Read more: 15 things your French ‘com com’ can do apart from collect your bins

How to septic tanks work

Septic tanks are claimed as a French invention, with Jean-Louis Mouras getting the first patent for one in 1881.

The concept is simple – waste water from toilets is piped to a tank that has two compartments, separated by a partition that allows some spill-over.

When a toilet is flushed, the contents arrive in the first compartment, the water settles, and solids start to sink to the bottom of the tank.

There, an­aerobic bacteria start to break down the solids into smaller solids and liquids, which spill over into the second tank.

Another round of breaking down takes place, while at the same time a drain from the tank leads to a soakaway for the water, which by now is much cleaner than when it arrived at the tank.

The four Ps

The main thing to remember about the system is it works best when only the four Ps are flushed down the toilet: pee, poo, puke and (toilet) paper.

Anything else risks clogging the system, either by causing a blockage in the pipe leading to the tank, or in the tank.

Nappies, sanitary pads, tampons, plasters and baby wipes are all well-known blockers, so if you have guests from town, it is worth having a talk about the system – and providing alternative means for them to cleanly dispose of these items.

Products to use with a septic tank

Care must be taken too when using bleach and some other household cleaners – they can kill the bacteria needed to break down the solids, and if the solids do not break down, they block the system.

In most rural areas, supermarket shelves have alternatives marked as suitable for septic tanks.

They also advertise a variety of products, such as Eparcyl, reputed to improve the efficiency of septic tank systems, either by balancing the water acidity to help bacteria or by adding bacteria.

Experts say a well-installed system does not need additives but experience shows they sometimes help reduce smells.

They do need emptying

Over time, the rate of build-up of solids becomes greater than the capacity of the bacteria to break it down, and the tank will have to be emptied.

Regulations, policed by the SPANC, determine how long a tank can operate before being emptied – typically, 10 years.

Sizes are set by the SPANC. Usually, a 3,000-litre tank is suitable for a four-person household.

Installing a septic tank

Local conditions determine the rules for soakaways.

On clay soils, which are fairly impermeable, the linear length of the soakaway will be longer than on light sandy soils, and you might need a greater depth of sand or gravel under the soakaway pipes.

Again, the SPANC will advise, and will also have to inspect any septic tank installation before it is covered up.

SPANC officials usually photograph the installation with a digital camera at this stage – it is easy for the location of tanks and soakaways to be forgotten.

DIY or pay a professional

If you have access to a mechanical digger and lifting equipment, installing a septic tank is something you can do yourself in most cases.

Kits cost around €1,500, to which must be added the cost of the digger (you can dig by hand if you have a week or two), at least three tonnes of sand (to bed and support the tank, and for the soakaway), and geotextile.

Professionals usually quote in the region of €3,500 to €5,000 – each system is different due to the layout of the site.

Things can get difficult if the site of the tank is lower than the site of the soakaway, or if you do not have a lot of land for your tank and soakaway.

In these cases, professionals can provide answers, using float-triggered pumps for the soakaways, and various clever methods of squeezing tanks and soakaways, or alternative filter systems, into small areas.

Inspection after 10 years

When 10 years from your last tank emptying have passed, SPANC will send you a letter announcing an inspection – cue for you to quickly arrange for the tank to be emptied by an authorised person, often a dairy or pig farmer, as they already have the equipment.

Expect to pay €100 to €200.

They will give you a certificate for the SPANC inspector.

Cheaper alternatives for emptying the tank exist, using oxygenating tablets and different bacteria to attack the solids, but are not recognised by SPANCs.

The inspector, whose visit will result in a bill for €100 or so, will look at the certificate and make a visual check of the system for things such as leaks from the tank, or trees growing into the soakaway.

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