Comment: Protecting water tanks from bacterial growth

By Mark Lemon, managing director of CSC Services

In this article, Mark Lemon, managing director of CSC Services, examines how water tanks can be effectively protected rather than replaced and how the installation of a regulated protective coating can not only reduce the risk of aquatic bacterial growth affecting water supply, but guarantee the lifespan of the asset

Legionella and Pseudomonas can be potentially harmful if allowed to breed in hospital water tanks

Pseudomonas and Legionella

Pseudomonas aeruginosa is an opportunistic pathogen that can cause a wide range of infections, especially in immunocompromised people.

The Pseudomonas outbreak in Northern Ireland hospitals in 2012, in which four babies died, focused attention directly onto hospital estates and facilities managers to test water systems and to put in place robust treatment plans should they detect any bacteria.

Without implementation of appropriate corrosion-control measures, water storage tanks will deteriorate, resulting in holes or possible structural failure

Pseudomonas bacteria often thrive in water systems, particularly large-scale ones such as those found in hospitals.

Older hospital buildings are particularly at risk when the water system is adapted for a change of use or to feed new buildings.

Where pipes are cut off they leave small dead ends where water can become trapped. This stagnant water is a known breeding ground for Pseudomonas bacteria.

Legionella bacteria are also commonly found in water.

The bacteria multiply where temperatures are between 20-45°C and nutrients are available.

Legionnaires’ disease is a potentially-fatal type of pneumonia, contracted by inhaling airborne water droplets containing viable Legionella bacteria.

Legionella control programmes are now carried out to prevent the growth of Pseudomonas species, and Legionella bacteria within water systems.

Risk assessments pinpoint ways in which Pseudomonas growth within water system can be minimised.

And flushing systems to prevent the stagnation of water within pipework is advocated across hospitals.

Mark Lemon

Why do water tanks corrode?

Corrosion is a complex series of reactions. It is the deterioration of a material that results from a chemical or electrochemical reaction with its environment.

Most water tanks are made of steel, a material highly susceptible to corrosion, which is accelerated by factors including the tank’s interaction with interconnected components, corrosive environmental conditions and stray electric currents.

Without implementation of appropriate corrosion-control measures, water storage tanks will deteriorate, resulting in holes or possible structural failure. Deterioration will lead to micro-aquatic bacterial growth including Legionella, Pseudomonas and a build-up of biofilm.

Control of micro-aquatic bacterial

The best way to avoid micro-aquatic bacterial growth is to line steel water tanks with a solvent-free approved coating proven to resist the growth of such bacteria. This is important for newly-commissioned tanks, or where tanks are refurbished.

When we work on tanks, they are first taken out of service. Grit blasting is then used to remove old coatings and to create a good surface profile on the steel, which aids adhesion and bond between substrate and the applied coating.

Even relatively-new tanks that are regularly cleaned and chlorinated can present problems, as many have cavities and cracks which often cannot be seen by the naked eye, but nevertheless harbour bacteria

Ultra-high-pressure water jetting (UHP jetting) is then used to remove coatings such as bitumen, epoxy, limpetite or polyurethane. The process can also be used to create a good surface profile on concrete.

All seams and intricate areas of the tank are ‘stripe coated’ prior to receiving a full coat of solvent-free polyurethane.

Where necessary, intricate areas would be ‘stripe coated’ again and a second coat of solvent-free polyurethane applied. The coating would be left to cure and set.

After full inspection, the tank would be cleaned again ready to go back into service.

In addition to resisting the growth of bacteria such as micro-aquatic organisms including Legionella, the coating would offer a high degree of flexibility, capable of accommodating structural movement.

Concrete tanks

Unprotected concrete tanks are prone to erosion. Concrete consists of micro-pores and if these are interconnected, causing a build-up of moisture and pollutants, problems will arise. Once the process of erosion starts, exposed aggregate can become more prominent, providing a potential harbouring ground for micro-aquatic bacteria.

Micro-pores and blow holes will provide an easy access route for water and chloride migration to any reinforcing steel. Under load, concrete will also crack providing further access points for micro-aquatic bacteria to breed.

Concrete tanks can be refurbished and relined. Any spalled area would be repaired and a cementitious coating applied to protect against water ingress and erosion.

There are various cementitious coating products which are approved. Cementitious coatings are also used as sealer coats on the damaged concrete to fill out blow holes or voids in the surface of the concrete, and in some cases to fill out the concrete returning it back to its original profile before a protective coating is applied.

An approved polyurethane coating would then be applied over this, providing full protection to the tank against erosion and micro-aquatic bacteria. Again, such coatings can be guaranteed when applied by an experienced contractor.

GRP water tanks

We cannot express enough the importance of having the correct protective lining installed,from the commissioning of the new tank to protect against bacterial growth from the outset

GRP tanks are common in hospitals and across healthcare estates. GRP sectional tanks are commonly used where access is restricted, or if replacement of a defective water tank involves structural alteration to the building.

Even relatively-new tanks that are regularly cleaned and chlorinated can present problems, as many have cavities and cracks which often cannot be seen by the naked eye, but nevertheless harbour bacteria. If water osmotic blisters are evident the tank should be examined immediately. If these blisters burst their contaminated toxic contents can be released into potable water.

Effective maintenance

We cannot express enough the importance of having the correct protective lining installed,from the commissioning of the new tank to protect against bacterial growth from the outset.

Once installed, protective coatings should be regularly inspected so that continuous levels of reliability and performance are maintained.

Companies