Water tank waterproofing seals drinking water, fire water and service water reservoirs and preserves the quality of the stored water. What sets it apart from other waterproofing work is this: here the waterproofing does not merely hold water back, it is in direct contact with it.
Contact suitability in drinking water tanks
Every material that will contact drinking water must hold a certificate of suitability for potable water contact. In a tank lined with an uncertified product the taste and odour of the water can change and a health risk arises.
Suitable products are generally cementitious coatings and crystalline systems. Bituminous membranes and solvent bearing coatings are not used in drinking water tanks.
Solutions by tank type
Buried reinforced concrete tank
A certified cementitious coating or crystalline system is applied to the inner face. Positive waterproofing against groundwater is also required on the outside. The tank is under pressure from the water inside and the ground outside, so both directions must be addressed.
Fire water tank
Contact suitability is less critical than for drinking water, but sealing performance and resistance to long standing water matter. Crystalline systems are advantageous here.
Roof or terrace mounted tank
Load and vibration raise the risk of cracking. Flexible, crack bridging systems are preferred. The terrace waterproofing beneath the tank must be assessed separately.
Critical details
Floor to wall junction. The most highly stressed point in the tank. A fillet must be formed and reinforced with corner tape.
Pipe penetrations. Inlet, outlet, overflow and drain pipes pierce the tank wall. Each penetration is resolved with a sleeve and waterstop.
Cold joints. Swelling profiles or waterstop strips must be placed in the joints formed between concrete pours.
Vents and access hatch. Surface water and contaminants must not enter around the cover. The cover must sit above surrounding ground level and be sealed.
Application and commissioning
The surface is cleaned and honeycombing and burrs are made good with repair mortar. Any active leak is cut off first. The waterproofing layers are then applied and the cure time stated by the manufacturer is observed.
Once curing is complete the tank is filled with clean water and leak tested. After the test the tank is emptied, the inner surface disinfected, and only then put into service. Filling before the cure time has elapsed damages the coating.
Frequently asked
Can it be done without emptying the tank
No. Work on the inner surface requires the tank to be emptied, dried and ventilated. The duration of the water outage must be allowed for in planning.
How often is maintenance needed
Tanks should be emptied, cleaned and visually inspected at regular intervals. Any cracking, blistering or loss of coating calls for intervention.
Is external waterproofing also necessary
For buried tanks, yes. Groundwater applies pressure from outside and can pass through the concrete and contaminate the stored water.
Once the type, location and intended use of your tank have been established on site, the appropriate certified system is selected.