Overhead water tank leaking
An overhead tank that loses water is usually cracking at the wall-to-base junction, where the restraint is greatest. Because the tank sits above occupied space, the leak shows up as damp on the walls and slab below rather than as a visible drip.
Not an emergency, but it will get worse and more expensive with every monsoon it survives.
Probable causes, ranked
Ordered by how often we find each one to be the actual source. The 'tell' is what distinguishes it from the others.
- 01most common
Cracking at the wall-to-base junction
The tell — Damp on the underside slab concentrated near the tank perimeter.
Overhead Water Tank (OHWT) Waterproofing → - 02common
Failed or absent internal lining
The tell — General damp across the supporting structure and visible deterioration inside the tank.
Food Grade Coating for Water Bodies → - 03common
Leaking inlet, outlet or overflow penetration
The tell — Staining traces to a specific pipe position.
Overhead Water Tank (OHWT) Waterproofing → - 04less common
Overflow discharging onto the terrace rather than to a drain
The tell — Wetting is intermittent and coincides with the tank filling.
Terrace Waterproofing →
Sixty seconds, before you call anyone
- Photograph it while it is actively wet. A dried stain tells a surveyor far less than a running one.
- Note whether it worsens with rain or with usage. Rain-linked points to the building envelope; usage-linked points to plumbing. This single distinction settles most arguments about responsibility.
- Check the area directly above and beside the damage, not only below it. Water travels along a slab before it drops.
- Look specifically for the tell of the most likely cause: damp on the underside slab concentrated near the tank perimeter.
- Do not chip into saturated plaster or paint over a damp patch. The first risks bringing material down; the second destroys the evidence needed to trace the path.
What it becomes if you leave it
Continuous wetting of the supporting slab and columns is one of the most reliable ways to corrode a building's structure, because it never dries out. It also wastes a great deal of water in a city where societies pay for it.
Often seen alongside this
- Water leaking from the ceiling in a top-floor flat
Water coming through a top-floor ceiling almost always originates on the terrace above — a lost fall, a failed waterproofing layer, or an untreated crack in the slab.
- Underground water tank contamination or loss
An underground tank that is losing water or showing contamination has a two-way problem: stored water escaping, and groundwater entering.
Overhead water tank leaking — questions we get asked
What is the most likely cause of overhead water tank leaking?
Cracking at the wall-to-base junction. The sign that points to it is: damp on the underside slab concentrated near the tank perimeter. That said, the ranking here is a starting point — the actual source is confirmed by survey, because more than one of these can be true at once.
What happens if I leave it?
Continuous wetting of the supporting slab and columns is one of the most reliable ways to corrode a building's structure, because it never dries out. It also wastes a great deal of water in a city where societies pay for it.
Can I diagnose this myself before calling anyone?
Partly, and it is worth doing. Photograph it while it is actively wet, note whether it worsens with rain or with usage, and check the area directly above and beside the damage. That single rain-versus-usage distinction narrows the cause more than anything else you can do in sixty seconds.
How urgent is this?
Act this season. Not an emergency, but it will get worse and more expensive with every monsoon it survives.
Send us a photograph and we will tell you what we think it is
WhatsApp a photo taken while it is wet, with a note on whether it tracks with rain or with usage. That is usually enough for a first opinion, and the site inspection that follows is free.
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