Wet rooms, balconies & swimming pools

Waterproofing of a Concrete Tank: Drinking Water, Certifications and the Correct System

Last updated: 12 October 2026

Waterproofing of concrete tanks using crystalline and cementitious products. Which materials are suitable for drinking water, application methods and curing tim

The system at a glance

Solutions & Applications · Cementitious Waterproofing Products

A cistern is the clearest example of waterproofing: there are no tiles on top; only water comes into contact with it — continuously, under pressure, and often from both sides if it is buried. This is where cementitious materials, which become part of the concrete, come into play. However, when the tank holds drinking water, a non-negotiable criterion is added: any material that comes into contact with the water must be approved for this use.

Firstly: what sort of water will it keep out?

Usage	What is required of waterproofing
Drinking water	Certification for contact with drinking water in every layer it comes into contact with; watertightness under positive pressure; if buried, also under negative pressure
Irrigation · firefighting · rainwater	Water tightness at the water column of the tank and resistance to fill-and-dump cycles
Wastewater · biological treatment	Resistance to chemically aggressive water — drinking water certification is not the criterion here

Drinking water: what each material specifies

Not all products claim the same thing. The table shows exactly what each product’s documentation states regarding drinking water:

Product	What is stated	Documentation
CERESIT CR 90	Approved for contact with drinking water	PZH HK/W/0321/02/2007 hygiene assessment — National Institute of Hygiene, Poland
VANDEX SUPER	Approved for contact with drinking water	NSF certification; also BBA
VANDEX BB 75	Approved for contact with drinking water	Refers to the product’s certifications
VANDEX UNIMORTAR 1	Certified for contact with drinking water	Refer to the product description
CERESIT CR 166 · CR 65	Drinking water tanks within the scope of application	No certificate mentioned
ESHAHYDROBENT	Non-toxic materials, suitable for storing drinking water	Declaration of suitability
VANDEX PLUG · CL 152 · CEMELAST 100	No statement regarding drinking water	Only under an approved layer

For public or municipal projects, or when requested by the supervising authority, the certificate must always be requested in writing, in its current version. ARGYNET provides this together with the technical data sheet and the declaration of performance.

Which system for which tank?

Case study	System	Why
New monolithic drinking water tank	VANDEX SUPER from within	Provides deep-penetrating waterproofing, does not delaminate, and remains permanently effective against new micro-cracks
Old tank, weathered or carbonated concrete	VANDEX BB 75	1.5–3 mm render, class R3, also protects the reinforcement
Buried tank in groundwater	Crystalline or BB 75	Operate under positive and negative pressure
Deep tank	CERESIT CR 90 or CR 65	Water column up to 15 m and 10 m respectively
Tank with cracks or movement, up to 5 m	CERESIT CR 166	Elastic, bridges cracks ≥ 0.5 mm

New tank: waterproofing begins during the concreting stage

Mass waterproofing compound — SINTOMIX SM N in concrete: a dense-pored, chloride-free compound, with tanks falling within its scope of application.
Bottom-to-wall joint — ESHAHYDROBENT or PVC Waterstop during construction. The waterstops are additionally treated with VANDEX SUPER using a brush (1.5 kg/m²).
Pipe penetrations — these are installed prior to concreting so that they do not need to be cut out later.

Step-by-step application

Open pores. Cleaning and removal of cement laitance, formwork oils and old coatings. Crystalline waterproofing works only on sound concrete with open pores — it does not rectify poor-quality concrete.
Repairs. Holes and delaminations are repaired; on surfaces that will come into contact with drinking water, use VANDEX UNIMORTAR 1, which is certified for this use.
Active leaks are first sealed with VANDEX PLUG and then covered by the approved layer.
Drainage channels at the bottom-to-wall corners using UNIMORTAR.
Moist substrate. Damp but not wet, with no standing water — the opposite of liquid-applied membranes.
Waterproofing. VANDEX SUPER: 1.2 kg/m² on the floor, 1.5 kg/m² in two coats on the walls. Or VANDEX BB 75 applied under pressure: 2–3 mm, 4–6 kg/m², in two coats.
Wet curing for 5 days — crystallisation requires water.
Filling. With VANDEX SUPER, not earlier than 7 days; with CERESIT CR 90, not earlier than 5 days.
Before being used for drinking water, the tank must be cleaned, rinsed and disinfected in accordance with the instructions of the relevant water supply authority.

Cladding and reinforcement

Where a smooth, easily washable surface is required, the SINMAST RM 22 epoxy paint is specified for the internal protection of drinking water tanks; for public use, its certificate is required. When applied over VANDEX SUPER, the paint may only be applied after 28 days and following surface etching with dilute hydrochloric acid — otherwise it will fail.

In tanks with corroded reinforcement or insufficient strength, repair must first be carried out using SINTOCRETE AntiCorr ST and SINTOCRETE (R4), and where specified by the structural analysis, reinforcement with S&P C-Sheet 240 carbon fibre fabric and SINMAST S2 WV resin on the outer wall.

ARGYNET Note

In a drinking-water tank, certification applies to every layer that comes into contact with the water — not just the main waterproofing layer. An approved crystalline waterproofing layer over an unapproved repair layer is correct; the reverse is not.

The choice between VANDEX and CERESIT is determined by the very same question that defines the category: what is coming from above. Nothing comes into the tank — only water. That is why the first choice is the system that becomes part of the concrete.

At ARGYNET, we specify the system for each tank, application and soil type; we provide the certificates and calculate materials per m².

Mistakes that cost

Incorrect	Consistency
Materials not certified for contact with drinking water	The tank has not been approved by the supervisory body or the water supply authority
Crystalline on a dry or sealed substrate	Crystallisation does not develop — the waterproofing remains superficial
No wet maintenance required	Cracks and material failure
Filling before the brochure’s publication date	The layer is loaded before it gains strength
Painting over crystalline coatings without neutralisation	Peeling paint
Joints without waterstops	Water passes through the joint, not through the mass