A single autumn downpour shows within fifteen minutes what was planned wrongly on a property: water stands on the paving, runs down the basement steps and finds its way across the terrace. For a landscaping business that is exactly the moment an enquiry starts — and it is a service that can be costed cleanly as soon as four input figures are on the table. This article shows how to build swales, soakaways, infiltration chambers and rainwater tanks into a service page of their own, which details make a quote calculable, and why the split stormwater fee is the argument that comes with a number.
Key takeaways
- German water law frames local infiltration of rainwater as the intended default. The service therefore does not sell as an optional extra but as the route the legislator has already mapped out.
- Whether a water permit is needed is decided by state law. In Lower Saxony, infiltration of roof, yard and path water on residential properties is exempt from the permit requirement under stated conditions.
- Four inputs make a quote calculable: connected area, soil permeability, groundwater level and the municipal fee bylaw. If one is missing, every figure remains an estimate.
- The split stormwater fee delivers the sales argument with a number: in Hannover the assessed area drops to 30 percent of the connected area once an infiltration facility is recognised.
- A separate service page per trade plus a pre-qualifying form reduces the follow-up questions that otherwise take several phone calls and a site visit.
Why rainwater is an enquiry topic right now
The ground your customers stand on is changing measurably. Settlement and transport area in Germany grew by an average of 50 hectares a day (Federal Statistical Office) between 2021 and 2024. The federal government's target, according to the same release, is below 30 hectares (Federal Statistical Office) as a four-year average by 2030. What runs as area statistics at national level lands on the individual plot as a very concrete question: where does the water go that the new driveway no longer absorbs?
Not every settlement area is sealed, but a large share of it is. The German Environment Agency puts the figure at around 45 percent (Umweltbundesamt) of settlement and transport areas; measured against Germany's total land area that amounts to 6.57 percent (Umweltbundesamt). The agency describes the consequence in one sentence that works well as the opening of a service page: sealed soil is covered so that it is airtight and watertight, which means rainwater cannot infiltrate, or only under difficult conditions.
The insurance industry writes the invoice for this. Natural hazards caused around 1.4 billion euros (GDV) in property insurance losses in Germany in 2025. Storm and hail accounted for the larger share: around one billion euros (GDV) across roughly 479,000 claims, or around 2,100 euros (GDV) per claim. Insured natural hazard losses outside storm and hail added up to around 400 million euros (GDV) across roughly 88,000 claims, with an average of around 4,700 euros (GDV) per claim — clearly above the figures for storm and hail. Since measurements began in 2002, these losses excluding storm and hail have cost insurers an average of 2 billion euros a year (GDV). At the same time, only around 59 percent (GDV) of residential buildings in Germany had included the additional module for flooding and heavy rain by 2025; the rest carry the risk themselves.
For your business that means there is an occasion, there is real pressure, and there is an audience that already knows it has a problem at the moment it searches. What is usually missing is a page that explains the matter in the language of the property rather than the language of a catalogue. How such an occasion turns into a steady flow of enquiries is covered in the article on unsealing as an enquiry driver; this text starts one level deeper and describes where the water stays afterwards.
Two figures that do not measure the same thing
What water law requires and what it does not
The starting point sits in the Federal Water Act and is worded surprisingly helpfully for a sales conversation. Rainwater should be infiltrated locally, be trickled away, or be discharged into a water body without mixing with foul water (section 55 (2) WHG). That is not an association recommendation but a statutory target provision. Quoting it on a service page shifts the baseline: infiltration is the intended route, discharge into the sewer the exception that needs justifying.
Niederschlagswasser soll ortsnah versickert, verrieselt oder direkt oder über eine Kanalisation ohne Vermischung mit Schmutzwasser in ein Gewässer eingeleitet werden, soweit dem weder wasserrechtliche noch sonstige öffentlich-rechtliche Vorschriften noch wasserwirtschaftliche Belange entgegenstehen.
That still does not answer the permit question. Introducing and discharging substances into water bodies counts as a use under section 9 (1) no. 4 WHG, and for a use the principle in section 8 (1) WHG applies: it requires a permit or a licence unless the Act or provisions issued on its basis determine otherwise. Section 46 (2) WHG contains exactly that exception for harmless infiltration of rainwater — but only insofar as a statutory ordinance under section 23 (1) WHG so determines.
In Lower Saxony, section 86 (1) NWG applies on top. Under it, no permit or licence is required where rainwater falls on roof, yard or path surfaces of residential properties and is to be infiltrated, sprinkled or trickled away on that property; for yard surfaces this only applies where infiltration passes through the biologically active soil zone. Other federal states regulate this differently, and a municipal bylaw may still impose a connection and use obligation despite the exemption.
| Case | Position under water law | What to clarify before quoting |
|---|---|---|
| Roof, yard and path water of a residential property, infiltrated on the same property (Lower Saxony) | No permit or licence under section 86 (1) NWG; for yard surfaces only through the biologically active soil zone | Soil conditions, groundwater level, the municipal bylaw |
| Infiltration covered by a statutory ordinance under section 23 (1) WHG | Exempt from permit under section 46 (2) WHG | Whether the state ordinance covers this specific case |
| All other discharges into a water body or into groundwater | Permit or licence required under section 8 (1) WHG | Application to the lower water authority, usually with sizing calculations |
| Commercial, car park and traffic areas | Regularly subject to additional treatment requirements | Specialist design and coordination before any figure is named |
A website does not replace legal advice and should not try to. What it can do is describe the sequence: who checks what, in which order, and at which point the lower water authority may enter the process. That description of the process takes the fear out of the official route, and it is the reason such pages lead to enquiries through the enquiry form more often than average.
Four construction types and what each stands for
Most customers know one word: soakaway. A good service page puts four construction types side by side, each with one sentence on where it fits and one on where it stops. The trade magazine SBZ has summarised the structure of the revised DWA-A 138-1 code of practice; the descriptions below draw on that.
Surface infiltration
Water is routed without interim storage directly onto adjacent, usually planted or partly permeable surfaces. It works without significant ponding and comes closest to natural infiltration (SBZ). It needs space and a permeable subsoil.
Infiltration swale
A shallow, planted hollow that briefly ponds the rainfall and releases it through the vegetated soil zone. It is visible, maintainable and can be worked into a garden design — and it is the type your customers actually understand after installation.
Swale-soakaway element
Swale on top, soakaway beneath, each with its own filling and emptying processes. Such elements typically offer high storage capacity and are therefore particularly suitable where soil permeability is low or space is tight (SBZ).
Infiltration chamber and tank
The chamber takes water at a single point into deeper, more permeable layers; the tank holds it back and releases it later to the garden or building services. Both complement infiltration through the soil zone rather than replacing it.
The choice is not a matter of taste but of two values from the on-site survey. For rainwater infiltration, permeability coefficients typically lie in a range from 10⁻³ m/s to 10⁻⁶ m/s (SBZ); sandy gravel, sandy silt and coarse, medium and fine sands are particularly suitable. If the soil falls below that, pure infiltration turns into a storage structure with throttled release — technically feasible, but a different calculation.
Clearances are a frequent point of dispute
Which details make a quote calculable
The difference between an enquiry that produces a quote in two days and one that sits for three weeks is usually eight lines of information. The following list is the short form of what belongs in a first conversation about stormwater management — and thus the field list for your form.
- Connected area in square metres, split into roof, terrace, driveway and path
- Surface finish of the paved areas; under the Hannover fee bylaw, concrete surfaces, bituminous surfaces, permeable paving, slab surfaces and gravel areas count as paved plot area regardless of the material used
- Permeability coefficient of the soil from an on-site survey, not from a general soil map
- Depth of the groundwater table and its range of fluctuation
- Type and depth of any basement plus the distance to neighbouring buildings
- Existing drainage: sewer connection, separate or combined system, position of the inspection chambers
- The municipal fee bylaw with its rates and its reduction provisions
- Machine access and the route for removing the excavated soil
These details translate into a multi-step form that does not ask everything at once. Step one clarifies the occasion, step two the surfaces, step three the subsoil, step four the location. The structure looks like this as data:
{
"step_1": {
"question": "What is this about?",
"options": ["Water pools after heavy rain", "New drainage on a new build",
"Checking a stormwater fee notice", "Rebuilding paving or a driveway"]
},
"step_2": {
"question": "Which surfaces need draining?",
"fields": {
"roof_area_sqm": "number",
"terrace_sqm": "number",
"driveway_sqm": "number",
"surface": ["concrete", "bituminous", "block paving", "slabs", "gravel"]
}
},
"step_3": {
"question": "What is known about the subsoil?",
"fields": {
"soil_survey": ["available", "not available", "unknown"],
"groundwater_level_known": ["yes", "no"],
"basement": ["with basement", "without basement"],
"existing_connection": ["separate system", "combined system", "no connection"]
}
},
"step_4": {
"question": "Where is the property?",
"fields": { "municipality": "text", "street_and_number": "text" },
"note": "drives the fee bylaw and the responsible water authority"
}
}Anyone who accounts for soil removal in the form already has the second largest cost item in view early; how to show it cleanly in the quote is covered in the article on excavated soil and disposal. And because an infiltration facility is rarely built on its own, the link to the paving service page belongs right next to it.
The split stormwater fee as an argument
Many municipalities split the wastewater charge into a foul water share and a stormwater share. The stormwater share is then measured by the built-over and paved area from which water reaches the central system. In Hannover the stormwater fee is 0.80 euros (Hannover fee bylaw) per square metre of chargeable area per year. That is not a large figure on paper — but across 200 square metres of connected area it comes to 160 euros a year, calculated on the Hannover rates and without any further assumption.
It becomes interesting at the reduction provisions. Where rainwater is demonstrably retained and partly infiltrated by an owner's own facility, and that facility is connected to the central system for the water it does not infiltrate, the assessed area falls to 30 percent (Hannover fee bylaw). The condition is a storage volume of at least 2.6 m³ per started 100 m² (Hannover fee bylaw) of connected area, and that the facility complies with code of practice A 138. A municipal bylaw therefore states what your quote has to deliver anyway — a very usable anchor for the sizing.
| Measure | Effect on the assessed area | Condition under the bylaw |
|---|---|---|
| Own infiltration facility with a connection for the water not infiltrated | Reduced to 30 percent | Storage volume of at least 2.6 m³ per started 100 m² of connected area, facility built to code of practice A 138 |
| Multi-layer green roof, properly built, with a build-up over 6 cm | Reduced to 50 percent | Intensive or extensive planting to the guidelines of the landscape development research society |
| Approved rainwater use system that produces foul water | Stormwater fee for the connected areas ceases to apply | Water meters, annual reading, declaration by the end of February; the foul water charge is levied instead |
| Full discharge into the central system | Full assessed area | 0.80 euros per square metre of chargeable area per year |
This table comes from a single bylaw and applies exactly there. Other municipalities set different rates, ask for different evidence or do not offer the reduction at all. The structure, however, is the same everywhere: there is an area, there is a rate, and there are provisions that make the area count for less. A business that explains on its website how to read the local bylaw holds an advantage that a pure price comparison does not show.
How the service page is built
A page on rainwater infiltration follows the same pattern as any other trade page, but with one particularity: it has to serve two motives at once — the acute damage and the planned investment. The following order has proven itself for both.
Occasion first
At the very top sit the three situations in which someone searches: water stands after heavy rain, a new build needs drainage, a fee notice is to be checked. Whoever recognises themselves reads on.
Construction types with limits
Four short blocks for surface infiltration, swale, swale-soakaway element and chamber or tank. One sentence per type on where it does not fit — that builds more trust than four lists of benefits.
Make the inputs visible
Show which four details you need before a figure is possible. That heads off the question about a square metre price on the phone and makes clear at the same time that you calculate rather than guess.
Address the fee question
A section of its own on the split stormwater fee with the local bylaw. It answers the unspoken question about the economic benefit without you having to promise a payback period.
Records and handover
What the customer holds at the end: measurements, photos of the installation, the facility details for the notification to the municipality and the maintenance notes. This is the section that reduces variations and callbacks.
At the very top sit the three situations in which someone searches: water stands after heavy rain, a new build needs drainage, a fee notice is to be checked. Whoever recognises themselves reads on.
Four short blocks for surface infiltration, swale, swale-soakaway element and chamber or tank. One sentence per type on where it does not fit — that builds more trust than four lists of benefits.
Show which four details you need before a figure is possible. That heads off the question about a square metre price on the phone and makes clear at the same time that you calculate rather than guess.
A section of its own on the split stormwater fee with the local bylaw. It answers the unspoken question about the economic benefit without you having to promise a payback period.
What the customer holds at the end: measurements, photos of the installation, the facility details for the notification to the municipality and the maintenance notes. This is the section that reduces variations and callbacks.
The page belongs in the same structure as your other trade pages — visible under services and with an entry point from the main page of your website. For businesses booked largely from the surrounding area, a look at local visibility pays off as well: rainwater is searched for locally after heavy rain, and demand arrives in waves.
Photos, records and what counts after handover
An infiltration facility disappears underground once installed. That is precisely why it is a photo subject: pictures of the open excavation evidence the scope of the work once the facility is buried. Collecting them properly yields material for the portfolio gallery and for the documents the customer submits to the municipality.
- Excavation and subsoil before installation, with a folding rule or tape measure in shot
- Filter chamber and inlet pipe once installed, before backfilling
- Soakaway body with the geotextile and the installed level visible
- Finished surface after the planting has established, framed like the first photo
- One sheet with the facility figures: area, storage volume, construction type, date
- A short maintenance note for the swale so that permeability is retained
During construction one point deserves emphasis, and the code of practice makes it explicitly: earthworks require protective measures against soil compaction and to maintain the permeability of the subsoil (SBZ). A swale base driven over by an excavator renders even a careful sizing ineffective — and the cause shows up in no photograph. Mentioning this on the website explains in passing why the work carries its price.
After handover begins the part many businesses give away. The facility needs maintenance, the municipality needs an area notification, and in autumn the swale needs a look. That becomes a recurring appointment once the website offers it — the system for that is described in the article on seasonal planning and in the guide to a quote that gets accepted. If you would rather not give the design work away, the reasoning sits in the article on charging a design fee instead of free plans; and because part of the labour cost can be tax-relevant for your customers, the article on section 35a tax relief is worth a look.
In the end, rainwater infiltration is a trade like paving or irrigation: technically well defined, economically calculable, and in need of enough explanation to justify a page of its own. Showing where the collected water goes afterwards connects it to irrigation as a service in its own right — and two separate jobs become one project. Good pictures for that do not happen by chance; what matters is set out under photos for your website.
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