Renovation or installation of a new septic tank in France

When you buy a villa in the South of France, you will most likely discover that many villas in the hills are not connected to a central sewer system. Each villa has its system, called a fosse septique, or septic tank. This may sound like you’re buying a house from the Napoleon era but is entirely normal. The most modern houses with the best sea views have this system. Simply because a connection to the sewer system only is available when you are in or nearby the city’s central sewer system.

Wastewater treatment is a legal obligation in France. The quality of the water is subject to strict monitoring and controls. Any dwelling, individual or collective, must have a wastewater disposal system that allows it to be cleaned up and discharged into effluents or the ground without polluting the environment or creating any health or environmental risk. “Wastewater” means: on the one hand, grey water, discharged by bathrooms, kitchen, washing machines, etc. on the other hand, sewage that comes from the toilets.

In France, about 25% of rural areas are not connected to the collective sanitary network. In this case, the property must have an approved device in the traditional sector of individual sanitation devices. It could be an all-water pit, a micro wastewater treatment plant, or a Phyto-purification plan. Phyto-purification is an individual, autonomous and ecological wastewater treatment solution that is easy to maintain and more economical than a septic tank. Particularly suitable for rural areas not connected to mains drainage, this purification process is simple to install, inexpensive and even aesthetic.

Phyto-purificatio is a natural process by plants to filter and clean up wastewater. Ecological and odourless, Phyto-purification consists of purifying wastewater using bacteria present in the roots of purifying plants (bamboo, reeds, cattails and sedges are the most used). This article explains how phytopurification for your French villa works.

Renovation or installation of a new septic tank in France

A septic tank is one of the autonomous wastewater treatment systems of the house and is checked by the SPANC. The SPANC (Public Service for Non-Collective Sanitation) is a local public service that is the municipality’s responsibility. Its missions can also be entrusted to service providers within the framework of a service contract or a public service delegation. The contact details of the SPANC in your area are available at your local town hall.

The system must carry out several on-site depollution phases: collection, pre-treatment (liquefaction), treatment (depollution) then discharge. Unlike the all-water tank, which collects all the wastewater from the house (black water + grey water), the septic tank only collects black water (toilets). The functioning of the septic tank is global: the tank retains solid matter and paper, which are transformed into sludge and gas. The water comes out clean and healthy.

These individual sanitation systems, therefore, make it possible to treat waste on-site without transport. The septic tank hosts a depollution process in three stages: liquefaction of solid and soluble matter, the transformation of sludge into acids transformation of acids into a gas (recyclable carbon harmless to the environment). The septic tank must meet particular standards and be installed according to the inhabitants: its volume and capacity are measured in PE (Human Equivalents).

Depending on the chosen method and the site’s characteristics, it is then connected to a micro-treatment plant or a spreading filtration system to discharge treated water into the ground. The septic tank operation is comparable to a solution for pre-treatment sewage. This device is no longer installed because sewage treatment with grey water is preferred. However, it is tolerated in some old homes still equipped with a septic tank in good condition. An all-water pit is gradually replacing it.

Buying an old property? Renew the fosse septique in one year

In the case of a septic tank upgrade (transformation of an old septic tank into an all-water tank), be aware that upgrading an all-water tank must be carried out quickly. After a visit to SPANC, the owner generally has four years to carry out the work to bring it up to standard, except in exceptional cases. But if the non-compliance of a septic tank is declared during the sale of a property, the purchaser of the property has only one year to carry out the compliance work.

Note that if your old model septic tank is less than 3m3, it cannot be renovated into an all-water tank. You have no choice but to replace it with a new pit and possibly recover your old pit as a rainwater collection pit, to water your garden, for example. You will then have to do an emptying, complete cleaning and disinfection.

Note that this is not recommended if your old pit is concrete. It is better to backfill this type of pit or have it deposited. Contact the recycling centre in your area to find out what to do with your old pit. The cost of bringing a septic tank into compliance can represent a large sum. This is always part of negotiating for your buyer agent when buying a property in France.

Cost of replacing a septic tank

The upstream soil study will be mandatory: 200 to 500€. Up to €1,000 if you ask the design office to help you put together your file for the SPANC.
An oil change will cost between 150 and 300 €. Count 500 € at least, if you also do a cleaning followed by disinfection.

A specialized company must carry out the emptying of an all-water pit.
The price to renovate the filter elements of a traditional die will depend on the die you have installed, which counts between 400 and 4000 €.
You will have to add between 5000 and 10,000 € additional corresponding to the price to renovate and replace a septic tank.
The price to change the non-collective sanitation system: count between 4,000 and 12,000 €.

Do the earthwork yourself to save some money
To save money if you decide to renovate your sanitation, you can, for example, evacuate the sand and the spreading network of your old sector yourself (it will only cost you to transport the waste to the waste disposal centre). However, in the future, it is best to entrust the installation of the new filtering to a professional.

You will then only pay 10% VAT and benefit from the guarantees of a professional company. Count around 3000-4000 € for the installation alone.

How do you know if the time has come to replace your pit and install a new one?

Depending on the sector, non-collective sanitation systems have an average lifespan of 10 to 25 years. The higher the starting quality (materials, installation, choice of filtering), the longer your septic tank will last.

In any case, it is challenging to keep a plastic tank for more than 25 years. A concrete tank is more durable, but it will be necessary to change some elements: pump, filters, fittings.
In any case, follow the manufacturer’s recommendations and do not hesitate to change the zeolite filter, the coco filter or the grease trap when the time comes.

Poor performance of these is the whole network and your pipes, which could saturate, clog and require a significant repair. Foul odours do not necessarily indicate that your septic tank needs to be renovated. On the other hand, a level of sludge that increases far too quickly or the surface above your pit that is subject to untreated rising water are signs that your industry needs a facelift!

How to replace a septic tank?

Here are the steps to replace a septic tank:

• Have a soil study carried out by a design office: approximately €500
• Apply for a building permit and declare the work to SPANC, which will come and check your installation and provide you with a validation document upstream: estimated cost €350
• Look for a company by comparing quotes for the 2021 upgrade of your septic tank
• Provide for the removal or backfilling of your old pit (you should fill an old pit), or the earthworks for the new one
• Provide the rainwater recovery system (in your old pit, cleaned and disinfected, or in a tank)

The estimated overall budget will be between 8,000 and 13,000 €

Installation of a new septic tank

Whichever device you choose, the cost of installing individual sanitation, whether new or renovating a septic tank, will be in the thousands of euros.

You can save a little by doing side work, grading or backfilling, but laying and connecting should be left to professionals.

To determine the total cost of an installation, nothing beats comparing quotes drawn up by professionals.

Installing a false all-water system will cost you no less than €10,000.

Pricing and options

For a spreading septic tank, count between €10,000 and €15,000, while a sand septic tank will cost you from €9,000 to €14,000. And every four years, the oil change will add €150 to €300. More info can be found here.

Ecological solutions using planted filters (Phyto-purification) are worth between €6,000 and €7,000 with dry toilets and up to €15,000 with conventional toilets. More info here.

The price for a small wastewater treatment plant starts at €6,000, depending on the number of users. More info on these ‘micro stations’ or mini-station d’épuration can be found here.