Knowledge base
Rainwater retention — obligation or opportunity for savings?
New regulations require rainwater retention on your property. Find out who is affected, how to choose the right tank, and how much you can save.
Retention in numbers
The maximum rate of the fee for reducing local retention, charged per cubic metre of rainwater discharged.
This is how much utility water in a household can be replaced by collected rainwater (irrigation, flushing, laundry).
From this year, tightened retention regulations apply to new developments and renovations on plots larger than 600 m².
A well-designed retention system allows the majority of the annual rainfall on a property to be managed on-site.
New retention regulations in Poland
Amendments to the Water Law Act and changes to building regulations are systematically tightening the requirements for rainwater management on properties. The aim is to reduce rapid stormwater runoff into the sewage system and lower the risk of urban flooding.
Property owners with a built-up area exceeding 600 m² who do not provide rainwater retention are subject to a fee for reducing natural local retention. This fee is charged quarterly by the mayor or city president.
For new developments, planning conditions and building permits increasingly include a requirement to design a retention system of a specified capacity, proportional to the sealed surface area of the plot.
The trend is clear — regulations will become stricter. Investing in retention today means not only avoiding penalties, but also future-proofing your property against upcoming regulations.
Who is subject to retention obligations?
The retention fee applies to owners of properties with an area exceeding 600 m² where more than 70% of the biologically active surface has been sealed. This applies to both businesses and private individuals.
In practice, this obligation covers: production and warehouse halls, logistics centres, retail facilities, car parks, housing developments, and increasingly also larger single-family homes on developed plots.
Municipalities are required to identify properties subject to the fee and charge it ex officio. This means that even if you have not received a decision so far, this may change as a result of updated records.
An exemption from or reduction of the fee is possible when the property owner demonstrates that they have water retention devices with a capacity corresponding to at least 30% of the maximum runoff from the property.
How do you select the capacity of a retention tank?
The required capacity of a retention tank depends on three factors: the sealed surface area of the plot, local rainfall intensity and the required retention time (usually calculated for a design storm of a specified return period).
As a rough guide, for a plot with a sealed surface area of 500 m² in central Poland, the minimum retention capacity is approximately 5,000–10,000 litres. For industrial halls with a roof area of 2,000 m², the requirement rises to 20,000–50,000 litres.
When selecting the capacity, it is worth considering not only the minimum required by regulations, but also the practical use of the collected water — for irrigating green areas, washing vehicles or industrial processes. A larger tank pays for itself more quickly through savings on mains water.
The designer of the retention system should perform calculations based on rainfall data for the specific location. Metal Zbiorniki supports clients in selecting the appropriate capacity at the enquiry stage.
Steel tanks vs. plastic tanks
The market offers retention tanks made from plastics (PE, PP) as well as steel. The choice of material is crucial for durability, capacity and operating costs over the longer term.
Plastic tanks are suitable for small capacities (up to 5,000 litres) and simple residential installations. Their limitation is low mechanical strength — in the case of underground tanks, they require careful backfilling and protection against soil pressure.
Steel tanks predominate in applications above 5,000 litres and wherever high structural strength is required — beneath car parks, manoeuvring yards or in ground with a high water table. Steel makes it possible to build tanks with capacities in the tens or hundreds of thousands of litres in a single module.
An additional advantage of steel tanks is the option of custom-dimension production, tailored to the available space on the plot. This is particularly important when refurbishing existing properties where space is limited.
Financial benefits and available grants
Investment in retention delivers tangible savings. Eliminating the retention fee means several hundred to several thousand zlotys per year for a typical commercial property. Using rainwater instead of mains water brings additional savings.
Many municipalities and Regional Environmental Protection Funds offer subsidies for the construction of retention tanks. The level of subsidy ranges from 50% to as much as 80% of the investment cost, depending on the programme and location.
For businesses, the costs of building a retention system constitute a tax-deductible business expense and can be depreciated. In the case of new developments, retention also increases property value and makes it easier to obtain building permits.
At current water prices (an average of 12–15 PLN/m³ including sewerage), a 10,000-litre retention tank in commercial use pays for itself within 3–5 years, with a service life of over 30 years.
Related products from our offer
Non-pressure underground water tanks
Steel tanks for rainwater and utility water storage, with capacities from 1,000 to 100,000 litres, available in above-ground and underground configurations.
View details →Above-ground single-walled tanks
Cost-effective steel tanks for rainwater retention, ideal for applications where a double-walled design is not required.
View details →Tanks for Individual Orders
Retention tanks designed and manufactured to individual dimensions, tailored to the site conditions and project requirements.
View details →Frequently asked questions about rainwater retention
Do you need a retention tank?
Contact us — we will help you select the right capacity and tank type for your property. Free quote within 24 hours.