Draining rainwater from a roof, a patio or a driveway is not just a matter of digging a hole in the garden. In western Switzerland, how it should be handled depends on the municipality, the type of soil and the water protection rules. This page helps you understand how a soakaway works, the questions to ask before starting and the points to clarify with a professional.
What is a soakaway and what is it for?
A soakaway, also called an infiltration well, is a buried structure that receives rainwater from a roof or a surface and lets it drain gradually into the ground. The water is therefore not sent to a sewer: it returns to the soil on site.
The principle is simple, but it works properly only under two conditions. The soil must be able to absorb water at a sufficient rate, and the water entering must be plain rainwater. If either is missing, the soakaway overflows or raises a water protection issue.
A soakaway is not the only solution. Depending on the plot, the water may instead be connected to the clean-water sewer, held in a tank, or infiltrated in a diffuse way. The choice does not always rest with the owner.
Infiltrate or connect: what your municipality’s PGEE says
The general drainage plan (PGEE) is the document through which the municipality organises water drainage across its territory. It states, for a given area, whether rainwater must be infiltrated or connected to a network.
To find out what applies to your plot, contact the municipality, usually the technical or planning department, or the relevant cantonal water protection department. Do not rely on what a neighbour did or on what used to be done: the rules change from one area to another, and from one period to another.
Ask precise questions:
- Is infiltration required, tolerated or ruled out on my plot?
- Is there a clean-water sewer that I can or must connect to?
- Is a permit required to install the soakaway or to modify the existing drainage?
- Which documents must be provided: plan, section, proof of permeability?
Soil permeability: the factor that decides everything
Even if the municipality allows infiltration, the soil has to cope. Sandy or gravelly ground readily absorbs water; clay, compacted or waterlogged ground in winter absorbs it slowly, or not at all. A soakaway in poorly permeable soil stays full, overflows when it rains and can flood a cellar or a patio.
Before deciding, you therefore need to know the soil. Depending on the scale of the project, this can range from a simple observation on site to an infiltration test, or even a soil survey carried out by a specialist. The municipality may also ask for supporting evidence.
A few observation pointers, to be treated as clues only:
- a puddle that lingers long after rain in the garden suggests poorly draining soil;
- water in a neighbouring excavation or a damp cellar points to a nearby water table;
- a steep slope towards the house calls for particular attention, because infiltrated water can come out elsewhere.
An earthworks professional often knows the soil of their region and can guide you, but this does not replace a test when the stakes are high.
What can go into the soakaway, and what must never
The basic rule is non-negotiable: wastewater never goes into a soakaway. This applies to water from toilets, the kitchen, the bathroom, the washing machine or the dishwasher. It belongs in the wastewater sewer, connected to the treatment plant. Sending it into the ground pollutes the water table and can make the owner liable.
What is meant for infiltration is rainwater from a roof or from a surface designed for it. Be careful with surfaces where the water picks up unwanted substances: an area where vehicles are washed, a place where products are stored, a busy road. The quality of water admitted for infiltration is a water protection matter, to be confirmed with the municipality or the cantonal department.
During a renovation, also check that no old connection, often invisible, mixes rainwater and wastewater. In an older house, a drainage plan or a camera inspection removes the doubt.
The steps of a soakaway project
A well-run project generally follows this order:
- Contact the municipality about the PGEE, the infiltration requirements and the permit.
- Assess the soil: observation, infiltration test or survey as appropriate.
- Locate buried pipes and utilities before any excavation, so as not to damage them.
- Have a quote drawn up detailing the excavation, the soakaway elements, the backfill, the connection and the reinstatement.
- Obtain the permit if one is required, before starting work.
- Build the structure: excavation, installation of the elements, filter layer, inspection chamber, connection of the downpipes.
- Check that it works after the first rains.
The order matters. Starting to dig before the municipality has replied means having to restore everything if infiltration is not allowed on your plot.
Who works on the site?
Depending on the layout, several trades share the work:
- Earthworks covers the excavation, the removal or reuse of soil and the backfill. Machine access to the garden, the presence of trees or walls, and the amount of soil to move all affect the preparation.
- Masonry is involved for the concrete or masonry elements of the soakaway and the inspection chamber, as well as for the connections and the reinstatement of the surroundings.
- Gutters collect the roof water and carry it to the structure, with a device to hold back leaves before they enter the soakaway.
On a small job, a single company may coordinate everything; on a more complex project, there may be several contractors. Ask in the quote who is responsible for what, in particular for the permit application and for restoring the ground.
Common mistakes to avoid
- Installing the soakaway without checking with the municipality. A non-compliant installation may have to be redone.
- Ignoring the soil. A soakaway in clay soil only stores water until it overflows.
- Placing the structure too close to a building. Infiltrated water can rise towards the foundations or a cellar. The distance to respect is something to discuss with the professional and the municipality.
- Connecting anything other than rainwater. This is prohibited and dangerous for the water table.
- Forgetting maintenance. Without a filter or an accessible inspection chamber, the structure clogs.
- Neglecting the overflow. In heavy rain, the water must be able to go somewhere without flooding your property or your neighbour’s.
- Not documenting anything. Keep the plan, the exact position of the structure and the supporting documents: they will be useful for a sale or future work.
What makes the cost of a soakaway vary
No serious price can be given without a visit or information about the plot. Here is what makes a quote vary:
- the nature of the soil and the depth needed to reach a layer that absorbs water;
- the roof or ground area to be drained, which determines the size of the structure;
- how accessible the site is for machinery;
- the amount of soil to remove or spread;
- the type of elements chosen and how they are installed;
- the length of pipework between the downpipes and the soakaway;
- the surfaces, plantings or paving to be taken up and then redone;
- the procedures, any soil tests and the plans to be provided.
Compare detailed quotes rather than totals: a quote that mentions neither the backfill, nor the inspection chamber, nor the reinstatement leaves grey areas.
When to call a professional
A soakaway affects water protection, the stability of the ground around the building and buried utilities. It is better to entrust the job to a company if:
- the ground is sloping or close to a building, a retaining wall or a property boundary;
- the soil is uncertain or the water table seems close;
- a permit is required;
- you do not know where the existing pipes run;
- an existing soakaway overflows, smells bad or no longer empties.
In that last case, do not try to patch it up yourself: the cause may be a blockage, saturated soil or a connection that should never have been there.
Preparing your quote request
The more precise your request, the more comparable the quotes will be. Gather:
- the address or municipality of the property;
- a description of what needs to be drained: house roof, outbuilding, patio, driveway;
- what you know about the soil and any water problems you have noticed;
- what the municipality told you, if applicable;
- photos of the garden, the downpipes and the access;
- your scheduling constraints and your reinstatement requirements.
You can then request a quote: describe your project online, and your request is passed on to craftspeople and companies in the region, who will contact you to prepare a free, no-obligation quote. The site does not carry out the work itself and does not choose the company for you: comparing offers and making the decision are up to you.
Updated 29 October 2026