Your own plot: holding rainwater back instead of draining it – guide

Editorial team·updated on 15 Sep 2026

Deadlines, funding rates, responsible offices, projects and events in this guide come live from our records. They are not written into the text and are not maintained twice.

With every heavy shower the water shoots off your roof into the downpipe and out of the city – and four weeks later you are watering with drinking water. In Berlin you also pay for that draining: the water utility's rainwater charge is calculated from the drained area. Holding rainwater on your plot is therefore the one greening step that shows up on a bill every year.

Your starting point

This guide assumes you can dispose over the plot: as an owner, as an owners' association, or with written consent. Tenants can put up a rain barrel; anything that involves digging belongs to the owner's side.

Four facts decide every solution. The connected area: how many square metres of roof and yard run into the sewer? The soil: Berlin stands on sand, which is good, but there are clay lenses and impeding layers – an infiltration test tells you more than a soil map. The groundwater level: in parts of the city groundwater stands high, and then infiltration works badly. And the site's history: where contamination is suspected, nothing is infiltrated.

Is this realistic?

There are four routes, and most plots combine two of them. Store: rain barrel or underground cistern, the water goes onto the garden. Infiltrate: swale, soakaway trench or shaft, the water goes into the groundwater. Delay: a green roof or retention roof holds back the runoff and evaporates part of it. Deseal: less paved area, less runoff – the most effective and most boring measure.

The nicest result is usually a rain garden: a shallow depression the downpipe drains into, planted with species that take both – wet for two days and dry for three weeks. It needs little technology, looks like a garden rather than a drainage installation, and relieves the combined sewer exactly where Berlin needs it most.

Not realistic: infiltration on an area smaller than a tenth of the connected roof area, infiltration right against the cellar wall, and a cistern that supplies the house with service water in summer without touching the drinking water installation. Professional planning is advisable as soon as you dig, and necessary where groundwater, cellars or neighbouring plots are involved. How Berlin projects have solved it:

Step by step

1. Work out area and volume Measure the connected roof and yard area. As a rule of thumb: Berlin's long-term average rainfall is a good half metre a year – so a hundred square metres of roof yields several dozen cubic metres of water. That figure decides whether a barrel is enough or a soakaway is needed.
2. Test the soil Dig a hole about fifty centimetres deep, fill it with water and see how fast it drains. Stopping point: if the water still stands after hours, infiltration is not an option at that spot – find another spot, or plan storage instead of infiltration.
3. Settle the permit question The lower water authority is your district's environment and nature conservation office. Ask there whether your infiltration is exempt under Berlin's exemption rules or whether you need a water permit. Stopping point: in water protection zones infiltration always requires a permit, and where contamination is suspected it is ruled out. You settle that beforehand, not after the excavation.
4. Keep the distances Infiltration installations need distance from buildings, cellars, trees, services and the property boundary – otherwise the water ends up in your own cellar or the neighbour's. This is where planning pays for itself.
5. Build the installation, or have it built A swale and a rain garden are hand work and one weekend. A soakaway trench, an infiltration shaft and an underground cistern mean machine excavation, geotextile, gravel or infiltration modules, an overflow and an emergency overflow. Plan the overflow: every installation also has to cope with the rain it was not built for.
6. Plant the rain garden properly In the depression, species that tolerate alternating wet and dry – purple loosestrife, yellow flag iris, meadowsweet, tufted hair grass – and drought-tolerant perennials at the rim. No peat substrates, no lawn. After two years the bed is dense and needs almost nothing.
7. Notify if you use it as service water If rainwater goes into the house – toilet, washing machine – that is a service water installation. Stopping point: it has to be notified, drinking and service water pipes must be strictly separated and marked, and a backflow preventer to the applicable standards is mandatory. None of this applies to garden use only.
8. Deregister the area with the water utility The step that brings money, and the only one nobody does for you: report the desealed, infiltrated, stored or greened areas to the Berliner Wasserbetriebe so that the rainwater charge is reduced. Depending on the management type the reduction ranges from a few per cent to full exemption.

Time and cost

Time: a rain barrel is an hour, a rain garden a weekend, a soakaway or cistern with the permit question and excavation two weeks to two months. The slowest part is the authority's answer – ask early.

Cost: editorial orders of magnitude, not quotations. A rain barrel with a downpipe diverter is in the tens to low hundreds of euros. A rain garden built yourself costs mainly plants, so a few hundred. Soakaway trench, infiltration shaft and underground cistern with excavation, installation and overflow are in the high hundreds to four figures, more for larger installations. We did not find reliable Berlin comparison prices for cisterns and soakaways – get two quotes rather than believing us.

Upkeep: low. Clean leaf traps and filters twice a year, look at the swale after heavy rain, keep the overflow clear, cut the rain garden once a year. The other side of the ledger: the Berliner Wasserbetriebe rainwater charge stands, according to its tariff page, at 1.809 euros per square metre of drained ground area per year. For a hundred square metres taken off the register, that is a permanent three-figure amount a year – which is why even a larger installation pays off here.

What are you allowed to do?

The principle. Under the Berliner Wassergesetz (Berlin water act), rainwater should as far as possible infiltrate through the biologically active soil layer, provided no danger to the groundwater and no significant harm to water bodies is to be expected. Those entitled to use a plot can even be required to infiltrate, retain or treat – rainwater management in Berlin is not merely permitted, it is the guiding principle.

When no permit is needed. Berlin's exemption rules take certain cases out of the permit requirement – among them uncoated roof areas up to a size in the low tens of square metres, and paths, yards and parking areas on residential plots, as long as no water-polluting substances are handled there. The exemption does not apply on contaminated or suspected sites. We state the rule, not its application to your plot: which variant applies to you is for the lower water authority to say.

When you do need a permit. In water protection zones infiltration always requires a permit, as it does for larger areas, for runoff from traffic areas and for coated metal roofs. The district's environment and nature conservation office acts as the lower water authority.

Two special cases. A service water installation in the house must be notified and is subject to drinking water hygiene rules: separate, marked pipes, a backflow preventer, regular servicing. A garden well in Berlin must be notified and, from a greater depth, requires a permit, and the notification must come well before the drilling – the state publishes its own leaflet for this.

Matching funding

There is no dedicated investment grant for private rainwater management in Berlin. The Berliner Entsiegelungsprogramm and BENE 2 address public, non-profit and commercial bodies. The financial lever for private individuals is therefore not a grant but the permanent reduction of the rainwater charge – graded by management type, with the largest effect for infiltration and desealing, a large one for green roofs and rainwater use, and a small one for storage alone.

Add a green roof and it becomes a funding case after all: GründachPLUS funds roof greening from a hundred square metres of vegetated area inside the funding area, and a retention roof is exactly the combination of retention and greening the programme is looking for. The Berliner Regenwasseragentur offers free advice, calculators and a directory of suppliers.

For soakaway, cistern and connection a specialist firm is worth it – overflow, distances and backflow protection are where self-building gets expensive:

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