A fire water tank is not always a structure for real estate tax purposes

Safety systems in modern buildings are not limited to access control systems or IT security measures. Regulations also require building owners to ensure fire safety for building users, which quite often means the need to maintain a water storage facility – most commonly in the form of a free-standing or underground tank. Efficient use of land often requires investors to design the water storage facility inside the building, i.e. within its structure, usually at the level of technical rooms. Can the construction solutions adopted have tax implications?

What the tax authorities think

In an individual tax ruling of 15 January 2026, the Mayor of Warsaw adopted a position unfavourable to the taxpayer. The authority considered that the space located in an office building and used to store fire water constitutes a structure erected inside another facility. One of the authority’s key arguments was that the main technical parameter of the disputed facility is its capacity and that the space is used specifically for storing water.

When there is a structure inside a building

It is generally accepted that structures built inside or on a building may be subject to real estate tax. However, it must first be established that the facility is a construction object separate from the building. Such separateness is not always clear or easy to prove. In such cases, tax authorities attach significant importance to information contained in the architectural and construction design and in administrative decisions.

Tanks as taxable structures

Until the end of 2024, the classification of structures was based on the provisions of construction law, under which tanks were expressly listed as examples of structures. However, since the beginning of 2025, tax law has had its own autonomous definition of a structure, which uses the term “tank” only in the context of a water treatment plant or a wastewater treatment plant.

This does not mean, however, that no tax is due on tanks located at commercial properties. Such facilities are currently classified as structures, among other cases, if they jointly meet the following two criteria:

1. a) functional condition: bulk materials, materials in pieces, or materials in liquid or gaseous form are or may be stored in them; and
   b) capacity condition: the basic technical parameter determining their purpose is capacity.

Three steps to verify whether a tank is a structure

Leaving aside water treatment plants and wastewater treatment plants, only those water tanks which jointly meet the following conditions are currently subject to tax as structures:

1. they were erected as a result of works consisting in construction, reconstruction, extension, superstructure, redevelopment or assembly to which the provisions of the Construction Law apply;
2. they jointly meet the functional condition and the capacity condition;
3. they are not a building or a part of a building.

If at least one of these conditions is not met, the tank is not subject to tax as a structure. Consequently, its value does not need to be included in the real estate tax return.

In practice, spaces inside a building which constitute rooms used to store water for fire safety purposes should be treated not as structures inside buildings, but as a component of the building as a construction object. Such a space filled with water, as part of the building, will be taxed not directly on its value, which would be very difficult to determine, but indirectly – as part of the entire building, based on its usable area. A separate issue is whether the area of such a water tank should increase the taxable usable area or whether, by analogy to shaft areas, it should be treated as so-called non-usable area.

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In case of doubts as to whether the scope of real estate tax has been correctly determined, contact MDDP. Our experts will provide comprehensive answers and advise on how to safely correct the tax return or assist in recovering overpayments.