Water Tank Leakage

What causes it

Overhead and underground tanks losing water through construction joints, cracks and failed internal coating.

Tanks are water-retaining structures governed by IS 3370, and the tolerance for defects is far lower than for a roof — a tank that seeps slightly loses thousands of litres a week and undermines whatever it sits on.

• Shell cracking — shrinkage and thermal cracks, most often at the wall-to-floor junction and at changes of section. Under a permanent head of water, a crack that would be harmless in a wall becomes a continuous loss.
• The kicker joint between base slab and walls, where the waterstop was omitted or displaced.
• Penetrations — inlets, outlets, overflow, scour and level probes, each a fitting cast or cored into a water-retaining wall and each a leak path if the flange was bedded on mortar rather than properly sealed.
• Failed internal render — a cement plaster lining that has debonded and is now holding water behind it rather than keeping it in.
• Overflow and lid detailing on overhead tanks, where the leak is often not the tank at all but water running down the outside from a badly detailed overflow or an ill-fitting cover.
• Movement in overhead tanks on slender supports, which cracks the shell at the base.

How we identify the real source

Water travels. The stain on a ceiling is frequently metres from the actual point of entry, which is why we deep-scan the structure before recommending treatment rather than working from the visible damage alone.

How we treat it

We begin with a measured loss test, because the first question is always whether the tank is actually the problem. A drop test over a fixed period, with inlet isolated and evaporation accounted for, separates a leaking shell from leaking pipework or an overflowing float valve — and a meaningful proportion of “leaking tanks” turn out to be neither.

Where the shell is at fault, the tank is drained and cleaned, the internal render removed if debonded, cracks cut out to a defined profile and any active water stopped with a plug mortar or PU injection. The wall-to-floor junction is coved and the shell reinstated with a polymer-modified structural mortar.

The lining is then a cementitious crystalline or polymer-modified cementitious system, applied in two coats at right angles at the specified coverage in kg per m², with reinforcing mesh at junctions and around every penetration. Crystalline chemistry suits tanks because it works with the permanent head of water rather than against it. Fittings are removed, re-bedded on proper flange seals and reinstated through the membrane rather than over it. Where the tank stores drinking water, a potable-water-approved system is specified and stated explicitly on the estimate.

The tank is refilled and monitored to IS 3370 over seven days, with permissible drop calculated against surface area, before it goes back into service and before the warranty is issued.

What it costs

Use the cost calculator for an indicative range, or book a free inspection for a written estimate.