Knowledge base
Drinking water tank — how to avoid contamination?
An incorrectly selected or maintained tank can be a source of drinking water contamination. Learn about the risks, PZH requirements and best practices.
Scale of risk
Estimated share of drinking water contamination incidents resulting from improper storage.
Every tank that comes into contact with drinking water must hold a PZH Hygiene Certificate.
Estimated number of EU illnesses linked to contaminated drinking water from various causes.
Recommended interval between inspections and cleaning of a drinking water tank.
Risk of water contamination in a tank — why does it happen?
A drinking water tank plays a critical role in the supply system — both in private buildings with their own water source and in small waterworks. However, the very act of storing water creates a risk of deterioration in water quality.
Water standing in a tank loses its residual chlorine, which prevents the proliferation of microorganisms. During warmer months, the temperature inside the tank encourages bacterial growth, including the potentially dangerous Legionella pneumophila.
Insufficient circulation, dead zones in the installation, lack of regular cleaning — these are the factors that turn a tank from a safety feature into a source of hazard.
The most common causes of water contamination in tanks
Improper tank material — tanks made from low-quality plastics or uncoated carbon steel may release harmful substances into the water. Corroding carbon steel alters the taste, odour and colour of the water, and above all provides a substrate for biofilm growth.
Lack of watertightness — leaking manholes, damaged seals and cracks allow contaminants from the surrounding environment to enter: dust, insects and rainwater. In underground tanks, the risk is particularly high.
Neglected maintenance — sediment, biofilm and limescale accumulate on the tank walls, creating an environment conducive to bacterial growth. Without regular cleaning and disinfection, water quality deteriorates steadily.
Improper temperature — tanks exposed to overheating (e.g. in an attic or a sun-exposed room) encourage the proliferation of pathogens. Temperatures of 20–45°C represent the critical zone for Legionella.
Lack of filtered ventilation — unfiltered ventilation allows dust, fungal spores and small insects to enter the interior of the tank.
Legal requirements — PZH certificate and beyond
Under Polish law, every material and product that comes into contact with water intended for human consumption must hold a Hygienic Certificate of the National Institute of Public Health (PZH). This applies to tanks, pipelines, fittings, and sealing components.
The PZH certificate confirms that the material does not release substances into the water at concentrations exceeding safety standards. The absence of a certificate means non-compliance with regulations and exposes both the installation owner and the contractor to legal consequences.
The Regulation of the Minister of Health on the quality of water intended for human consumption defines the microbiological and physicochemical parameters that water must meet at the point of collection. The installation owner is responsible for maintaining these parameters throughout the entire network — including storage tanks.
For pressure tanks, an additional requirement is approval by the Office of Technical Inspection (UDT) and regular periodic inspections.
Choosing the right tank material — the key to safety
Stainless steel (AISI 304, 316L) is the material of choice for drinking water tanks. It does not corrode, does not release substances into the water, is easy to clean and disinfect, and its smooth surface inhibits biofilm formation.
Tanks made of food-grade stainless steel meet PZH requirements without the need for additional internal coatings. This is a more durable and, in the long term, more cost-effective solution than coated tanks.
Tanks made of plastics (PE, PP) are a popular alternative in smaller installations. However, they must hold a PZH certificate, and their service life and resistance to external conditions is limited compared to stainless steel.
Regardless of the material, the tank should be equipped with a sealed inspection manhole, a filtered air vent, connections enabling full draining and cleaning, and a level indicator.
Maintenance and upkeep — best practices
Regular cleaning and disinfection — recommended every 6–12 months, depending on source water quality and operating conditions. This includes draining, mechanical sediment removal, chemical disinfection, and rinsing.
Leak-tightness inspection — regular inspection of manhole seals, nozzles, and connections. Gasket replacement in accordance with the manufacturer's schedule.
Temperature monitoring — particularly important during summer months. Tanks exposed to heat should be thermally insulated or relocated to a cooler space.
Water quality testing — periodic laboratory tests (microbiological and physicochemical parameters) are the only reliable way to confirm that the water in the tank meets the required standards.
Maintaining an operation log recording cleaning dates, test results, and repairs carried out facilitates installation management and is required for public water supply systems.
Related products from our offer
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PZH-certified drinking water storage tanks. Various capacities and configurations.
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Stainless steel hot water tanks with protection against Legionella growth.
View details →Do you need a drinking water tank with PZH certification?
Contact us — we will advise you on selecting the right tank and material for your installation. No-obligation quote.