Water tank leaking or losing water? Find out where, then fix it
A leaking tank shows up as a drip below an overhead tank, a damp patch on the ceiling under it, or a level that drops when nobody is using water. The first job is to prove it is the tank and not a valve, float or pipe. Then the repair depends on whether it is one spot or the whole lining that has failed.
Published · Updated
Signs you will notice
- Drips or damp patches on the slab or wall below an overhead tank
- Water level falling overnight with all taps closed
- Damp ground or walls around an underground tank (sump)
- Cracks or peeling lining visible inside the tank when it is emptied
- The motor running more often than before
Where the water usually comes from
Often more than one source is at work, and each needs its own fix.
Cause 1
Overhead tank dripping in one spot
One or two drip points at the base or wall of an overhead tank. The rest of the tank looks sound.
Check it yourself: With the tank full, mark each drip point with chalk. Check again with the tank half full: drips that stop are above that level.
How it is usually fixed: Inject each drip point from outside with PU foam followed by PU resin.
Cause 2
Overhead tank leaking badly
Leakage from many points on an overhead tank, or damp spreading widely beneath it.
Check it yourself: Empty the tank and look inside for cracks, hollow plaster and a lining that has peeled away.
How it is usually fixed: Strip the inside back to concrete, apply a flexible cementitious waterproofing coat, replaster and finish with a lining rated for drinking water.
Cause 3
Underground tank losing water
An underground or ground-level tank loses water even though nothing is drawn from it.
Check it yourself: Close the inlet and every outlet, mark the level and check it after 12 to 24 hours. A drop means the tank itself is leaking.
How it is usually fixed: Strip back to concrete, inject the cracks, apply a flexible cementitious waterproofing coat, replaster and finish with a lining rated for drinking water.
Cause 4
Water tank lining worn out
An old tank with a worn, flaking lining, even if the concrete is still sound.
Check it yourself: When the tank is cleaned, see whether the lining comes off in flakes or the plaster is powdery to touch.
How it is usually fixed: Strip the old lining, apply a flexible cementitious waterproofing coat, replaster and finish with a lining rated for drinking water.
Methods follow proven, manufacturer-approved waterproofing systems. The right one for your building depends on what is found on site.
What a photo can and cannot tell you
Photo guidance points to the likely source. It is not a confirmed diagnosis.
A clear photo can show
- Where it drips and what the outside of the tank looks like
- Cracks on the tank walls or base
- The inside lining, if the tank has been emptied
A photo cannot settle
- Leaks below the water line inside a full tank
- Whether a valve or pipe inside the tank is leaking
- Whether the current lining is safe for drinking water
Simple checks before you call anyone
- 1Rule out the float valve and overflow first: watch whether water is running out of the overflow pipe.
- 2Do the level-drop test with inlet and outlets closed.
- 3Mark drip points with the tank full and again half full.
- 4Photograph the tank outside, the drip points and, if emptied, the inside.
When you need someone on site
- An underground tank keeps losing water
- You cannot locate the leak with the tank full or half full
- The tank itself is cracked through
Where Membrain works on site, a site diagnosis confirms the source, and thermal imaging finds hidden leaks before anything is broken. The app checks whether your pincode is covered.
Common mistakes that waste money
- Coating the inside with a product not meant for drinking water.
- Patching from outside only when the whole lining has failed.
- Filling the tank again before the repair has cured.
- Ignoring pipe entries, which are a common leak point.
Before you accept a contractor's quote
- Does it say whether the tank will be injected at points or relined fully?
- Is the final lining suitable for potable (drinking) water?
- Are pipe entries and the tank-slab corners included?
- Is a water-hold test planned before handover, and how long is the curing time?
Already have quotes? Membrain can compare them on scope, not just price. Planning the work instead? A written specification makes quotes comparable.
How this guide is built
Diagnostic basis
Membrain separates visible signs from possible water-entry mechanisms, then asks for evidence that can distinguish the remaining causes.
Repair-source governance
Public guides stay brand-neutral. When Membrain creates a repair plan, methods and products come from current approved manufacturer documents in its technical library.
Evidence limits
A photo cannot confirm concealed pipes, waterproofing layers or moisture depth. When remote evidence cannot separate the causes, a site inspection is the correct next step.
Technical notes behind this guide
Deeper reasoning on the moisture patterns and water-entry mechanisms used to interpret this problem.
Paani ki tanki se leakage kaise pakdein?
Tanki ke neeche tapakna, chhat pe daag, ya bina use kiye paani kam hona, ye sab leakage ke nishaan hain. Pehle pakka karo ki leak tanki ka hai, valve ya pipe ka nahi.
Inlet aur saare outlet band karke paani ka level mark karo aur 12 se 24 ghante baad dekho. Andar ki coating hamesha peene ke paani ke liye safe honi chahiye.
Frequently asked questions
Can a tank leak be fixed without emptying it?
Isolated drip points on an overhead tank are often injected from outside. A tank that leaks widely has to be emptied, stripped and relined.
Is the repair safe for drinking water?
Only if the final inside lining is a product rated for potable water. Ask for the product name and check it is meant for drinking-water tanks.
How long before I can use the tank again?
It depends on the system and its curing time. Your contractor should give a written date and a hold test before you start using it.
Why does the ceiling under my overhead tank stay damp?
Often the tank base or a pipe entry is leaking. Check it with the tank full and again after draining it below the suspected level.
Not sure which one it is?
Share a photo and answer a few questions. Membrain shows the likely sources and a repair plan built from proven waterproofing methods, in minutes. Free to start.
Remote guidance, not a site inspection.