Finding a crack in a water storage tank is an immediate concern due to contamination, compliance and cost.
However, a cracked water tank can almost always be repaired. Repairing a water tank crack restores the tank’s structural integrity, stops leaks and extends its working by many years.
Replacing a water tank is only necessary when the tank has suffered catastrophic structural failure.
COVAC has been carrying out concrete tank repair, GRP repair, and steel tank repair across the UK for over 25 years.
What Causes Cracks in Water Tanks?
The most common causes of cracks in water tanks are:
Age and general wear.
All water tanks degrade over time. Concrete becomes porous, steel corrodes and GRP resin breaks down. Cracks in a water tank most often appear simply because a tank has reached the end of its unprotected service life
The freeze-thaw cycle.
Water that penetrates a tank wall expands when it freezes and contracts as it thaws. Over repeated cycles, this movement opens up hairline cracks and widens existing ones. This is particularly common in concrete water tanks in exposed locations.
Ground movement and settlement.
Soil shifting beneath or around a buried or ground-level tank creates stress across the structure. Even minor settlement can cause cracking in rigid materials such as concrete
Chemical attack.
Aggressive water chemistry, cleaning chemicals and industrial effluents can degrade tank materials from the inside, weakening the structure and causing surface cracking and spalling.
Mechanical impact.
Physical damage from vehicles, falling objects or heavy equipment working near the tank can cause immediate cracking or fractures
Poor original construction or inadequate lining.
Tanks that were never properly lined or were lined with non-approved materials are more vulnerable to early degradation and cracking as the substrate deteriorates
Concrete is a naturally porous material. Unprotected concrete tanks will absorb water over time, leading to erosion, deterioration, and eventually cracking. This is not a sign of failure. It is a predictable outcome of an unlined concrete tank reaching a certain age.
Does the Water Tank Material Affect the Way It Is Repaired?
Yes. The way to repair a water tank depends on its construction material. The three main tank types in UK water storage are concrete, GRP (Glass Reinforced Plastic) and steel. Each develops cracks differently and requires a specific approach to restore it correctly.
All three can be repaired effectively when the damage is caught at the right stage. The key across all tank types is that repair must be followed by a high-performance protective lining to prevent the same damage recurring.
COVAC repairs all three tank types. Visit our service pages for concrete tank repair, GRP tank repair, and steel tank repair for full details on each service.
How Is a Cracked Concrete Water Tank Repaired?
Repairing a concrete water tank is one of the most common services COVAC carries out across the UK. Concrete tanks are found in commercial buildings, tower blocks, water treatment facilities and a wide range of industrial and institutional settings. They are durable structures, but without proper tank lining, they will degrade.
The repair process for a cracked concrete tank follows a structured sequence. Skipping any surface preparation is the most common cause of repair failure.
- Full inspection and condition assessment: The tank is drained and inspected internally. The extent of cracking, spalling and any reinforcement corrosion is assessed before a repair specification is drawn up.
- Surface preparation: Damaged concrete is cut back to a suitable substrate. Loose material, contamination and any previous non-approved coatings such as bitumen or asphalt are fully removed.
- Structural crack repair: Cracks are routed out and filled using specialist cementitious or resin-based repair mortars. Exposed reinforcement bars showing rust staining are treated and encapsulated to prevent ongoing corrosion.
- Surface reprofile: The internal surface is re-profiled to create an even substrate ready for coating.
- Application of WRAS-approved lining: COVAC’s Acothane DW coating is applied to the full internal surface, creating a non-porous and chemically resistant barrier that prevents future water ingress, microbial growth and further deterioration.
- Final inspection and handover: The completed repair and lining are inspected before the tank is returned to service. All work is backed by a minimum 10-year guarantee.
Many older concrete water tanks contain non-approved coatings such as asphalt or bitumen. These must be fully removed before any repair or relining can take place. Applying a new lining over a non-approved coating causes adhesion failure and invalidates the guarantee. COVAC’s Acothane DW coating system is WRAS certified and DWI listed, meaning it is fully approved for contact with potable water.
View our completed projects in our concrete water tanks case study.
How Is a Cracked GRP Water Tank Repaired?
A cracked GRP water tank repair addresses the specific failure modes of glass reinforced plastic tanks. GRP tanks are widely used for potable water storage across the UK due to their light weight and resistance to corrosion. But over time, the resin matrix that binds the glass fibres degrades and cracks.
GRP cracks are often surface-level at first. Left untreated, they allow water to penetrate and cause deeper structural damage.
- Cracked or crazed areas of GRP are ground back and the damaged laminate is removed to a sound edge
- New GRP laminate is applied to rebuild the structural integrity of the repaired area
- The full internal surface is prepared and the WRAS-approved Acothane DW coating is applied to seal and protect the tank going forward
- Panel joints and seals are checked and resealed as part of the same operation
View our full GRP tank repair service and our GRP tank case studies for real examples of completed repairs.
How Is a Cracked Steel Water Tank Repaired?
Repairing cracks in a steel water tank involves addressing corrosion-related cracking and any failures at seams, panel joints or around fittings. Steel tanks corrode from the inside when the protective lining fails or were never in place. Corrosion spreads rapidly and can cause pinhole leaks and cracking at joints.
The repair process for steel tanks depends on whether the tank is a galvanised flat steel tank, a pressed steel sectional tank or a welded fabricated tank. The approach varies, but the principle is the same in all cases.
- Corroded areas are blast-cleaned or mechanically prepared to remove all rust and contamination
- Holes and cracks are repaired using appropriate welding or plate bonding techniques
- Panel joints and connections in sectional tanks are resealed as part of the repair scope
- The full internal surface is coated with Acothane DW to provide long-term corrosion protection and a hygienic and potable-water-safe finish
View our steel tank repair service for more details.
Repair or Replace a Cracked Water Tank: How Do You Decide?
Water tank repairs cost significantly lower than replacement when you account for the full cost of a new tank, including drainage, disposal, installation, and the disruption of taking a water system offline. Repair also preserves an existing structure that, with a quality lining applied, can last for decades more.
| Situation | Likely Outcome | Action |
| Hairline cracks, surface crazing or minor spalling | Fully repairable in a single operation | Repair |
| Active leaks at panel joints or fittings | Repairable. Joints resealed and surface relined | Repair |
| Corrosion pinhole leaks in steel tanks | Repairable if caught before widespread structural loss | Repair |
| Concrete cracking with exposed reinforcement | Repairable. Reinforcement treated and concrete re-profiled before relining | Repair |
| GRP delamination affecting structural integrity | Requires detailed assessment. Partial or full laminate rebuild may be needed | Assess |
| Widespread corrosion throughout steel structure | Requires detailed assessment. May depend on the extent of material loss | Assess |
| Catastrophic structural collapse or failure | Replacement is likely the only option | Replace |
At COVAC, we would recommend replacement over repair are those where structural failure has been so severe that repair would not be safe or cost-effective.
What Are the Signs a Water Tank Needs Attention?
Many water tanks show warning signs before a crack becomes a serious problem. Catching damage early keeps repair costs down and reduces the risk of water quality issues or compliance failures.
- Visible cracks or crazing on the internal walls, base or roof panels of the tank
- Active leaks or damp patches on the exterior of the tank or surrounding structure
- Rust staining on concrete tank walls, which indicates that the reinforcing steel bars beneath are corroding and expanding
- Changes to water appearance, taste or odour, which can indicate that tank material is leaching into the stored water
- A tank that has never been inspected and is more than 15 to 20 years old.
- Failed inspection results relating to structural condition, water quality or hygiene
- Previous non-approved coatings such as bitumen or asphalt that are now flaking or contaminating the water
Regular water tank inspection is the best way to catch problems early. COVAC offers inspection services nationwide. Our water tank inspection hatch installations make future inspections simpler and more thorough.
You can also read our article on whether tank repairs can improve water quality and our guide to tank lining types, materials and regulations.
Found a Crack in Your Tank?
COVAC has been carrying out water tank crack repair and full water tank refurbishment for over 25 years. Every job follows the same structured approach, regardless of tank type or size.
Find out more about our approach on the COVAC coating system page and our what we do page. We cover every region of the UK, including Southern England, London, the Midlands, Northern England, and Scotland.
For any repair or relining jobs, we respond quickly to repair enquiries across the whole of the UK. Contact us today to get a free, no-obligation quote from our specialist team.
