In a tank for drinking water or a food product, the lining likewise protects the contents more than the steel. But those contents have a property fuel does not: a human consumes them. So the internal lining takes on a requirement found nowhere else — it must not merely be chemically resistant but safe for health, and it must carry a document proving it. Here is what that changes in material selection and in handover.

Why water and food are a separate case

In a tank for an aggressive medium we protect the steel from the contents. In a fuel tank the task is already the reverse — to protect the contents from the lining. With drinking water and food products it is the same as with fuel, but with an even higher cost of error: whatever the lining releases into the water or product ends up in a person.

Water itself is a non-aggressive medium; ordinary drinking water is gentler than many technical media. In terms of chemical resistance the task is easy. The difficulty lies elsewhere: the lining has no right to introduce into the water anything that changes its composition, taste, odour or safety. This requirement is not mechanical and not about “resistance” — it is hygienic.

★ To be explicit: the key distinction of this task is not the properties of the material but the existence of a permitting document specifically for contact with drinking water or food. A material may be as resistant as you like, but without such a document it is unsuitable for this task. That is why this article is built around the document, not around the type of binder.

What is required of the lining

From the objective of “do no harm to what a person will drink or eat” follow requirements, all of them verifiable.

A permitting document for contact with drinking water or food — for this specific product. Not a “food-grade coating type” in general, but a specific material with a sanitary conclusion that it is safe for such contact. This is the first thing to request, and without it the discussion does not proceed.
No migration of harmful substances. A fully cured lining must not release binder components, solvents, plasticisers or pigment into the water or product. This is verified by leaching (migration) tests: an extract from the lining is analysed for the content of regulated substances.
Organoleptic neutrality. For drinking water, taste, odour and colour are regulated. The lining must not give the water a taste or smell — a separate, testable parameter, not a trifle.
Resistance to disinfection. Drinking water is chlorinated or ozonated. The tank lining must withstand the adopted disinfection regime without breaking down or beginning to leach afterwards.
Light colour and continuity with no pores. As in other tanks: on a light lining an inspection reveals sediment and defects, and a pore is a point where water contacts bare steel and picks up corrosion products.

Permitting documents — how approval works

This is the central question of the topic, so it gets its own section, with no guesswork.

In Uzbekistan, the contact of materials with drinking water is the remit of the sanitary-epidemiological service (the State Sanitary-Epidemiological Surveillance bodies of the Ministry of Health). The quality of drinking water and the requirements for it are set by sanitary rules and norms; the owner of a drinking-water supply system is obliged to coordinate its operation with the sanitary service. The practical meaning for our task: the internal lining material must hold a sanitary-epidemiological conclusion of suitability for contact with drinking water, issued on the basis of a hygienic assessment. This is the same mechanism as with aviation fuel: approval is granted not by a “standard on the material type” but by a conclusion from testing of the specific product.

International systems are arranged the same way, and it is worth knowing them because manufacturers often cite them. For drinking water there is, for example, the NSF/ANSI 61 standard: what is certified is not an “epoxy coating in general” but a specific product, which undergoes extraction testing and confirms that in the cured state it does not release harmful substances into the water above the permitted level. For food contact there are separate frameworks — the US requirements for polymeric food-grade coatings and the European Union regulations on materials in contact with food. Different systems, but everywhere the principle is one: a document for the specific product plus migration testing.

★ I deliberately give no specific limit values, clause numbers or methods here: they are in the document itself and in the conclusion for the material. The correct course of action is not to look for a “norm on coatings in general” but to request from the supplier a document on the suitability of its specific material for contact with drinking water or food.

Surface preparation

The same requirements as for any critical internal lining, with no concessions. Cleanliness grade — Sa 2½ as a minimum, Sa 3 for critical duties, to ISO 8501-1, with checks on profile, soluble salts and dust.

In addition to the usual sequence — the same as for aviation fuel: before work begins the tank must be cleaned of residues of any previously stored product. If the vessel formerly held something technical, traces of it in the pores of the old coating and in the welds are a direct threat to the future drinking water.

Application and curing

The application technique is the usual one for internal linings: control of steel temperature and dew point, a margin above dew point, observance of overcoating intervals, forced ventilation during application and curing.

And the same critical point as for aviation fuel, only the cost of error is even plainer. The lining must be fully cured before any water or product enters the tank. An under-cured lining releases residual solvent and unreacted components into the contents — precisely what all of this protects against. Full cure times are stated by the manufacturer, depend on temperature, and cannot be shortened to suit a construction programme.

Before commissioning, a drinking-water tank is flushed and disinfected, and then a control water sample is taken. This is the final step that confirms the lining really does not affect the water under real conditions.

Handover: what the documentation must contain

A sanitary-epidemiological conclusion (or other permitting document) for the material for contact with drinking water or food — from the manufacturer, before work starts.
Cleanliness grade to ISO 8501-1 with records, profile, soluble salt test, dust — before the first coat.
Application conditions logged: steel and air temperature, humidity, dew point for each work area.
Dry film thickness over a grid of points.
Holiday detection over the whole surface.
Confirmation of full cure before commissioning.
Flushing, disinfection and a control water sample before start-up — to sanitary requirements.

The absence of any one of these documents means the tank has been accepted as a formality. For drinking water and food this is not bureaucracy: here the chain of sanitary safety begins with the very surface the product touches.

In brief

A tank for drinking water or a food product differs from the rest not in the aggressiveness of the medium but in the fact that a person consumes the contents. Three rules therefore apply. The material is chosen only with a permitting document specifically for contact with drinking water or food — by a document for the specific product, not by the type of binder. The lining is made light in colour and continuous, so that a defect is visible. And it is allowed to cure fully before water or product is admitted — and before start-up the tank is flushed, disinfected and verified by a sample.

Coatings for drinking water and food products: material selection and permitting documents