Hot & Cold Water Systems
Hot & Cold Water Systems

Hot and Cold Water Systems

Within the world of water treatment, hot and cold water systems are the most commonly found systems in commercial properties. A hot and cold water system, also known as a domestic water system, is the system on a site that distributes hot and cold water to a number of outlets such as taps, toilets and showers.

Historically, hot and cold water systems were the most common culprit for outbreaks of Legionnaires’ disease, with more cases being caused each year by hot and cold water systems than cooling towers. However, thanks to better maintenance and the stricter treatment regimens laid out in the HSE’s ACoP L8 there have been very few Legionnaires’ disease outbreaks caused by hot and cold water systems in recent years.

Types of Hot & Cold Water System

It is important to understand the range of system types and the different approaches to adopt when treating them, to ensure that the most effective water treatment regime can be employed. The following is an overview of the most common hot and cold water systems found in industrial properties including what the systems are comprised of; the risks that they pose, problems you may encounter and the ways in which we can help you to ensure your hot and cold systems water treatment regime is as effective as possible. There are three main types of hot and cold water systems as follows:

Gravity System with Recirculation

A gravity system with recirculation is the most common design of a hot and cold water system and can be found in the majority of commercial buildings. The system is called a gravity system because the water flows down within the system by gravitational pull, and water pressure at the tap, (or any other release point) is dependent on the height of the cold water storage tank in relation to the tap. Outlets that are furthest below the storage tank have higher pressure as a result of the gravitational pull. 

The circulation of hot water is continual within the system in a loop where hot water passes to all of the hot water outlets before re-entering the hot water calorifier to be reheated. The reason that the hot water circulates in this way is so that hot water can be quickly available at any outlet, regardless of its distance from the calorifier. When hot water is used from the outlets the calorifier will be refilled from the cold water storage tank. Other than that hot water should continue to circulate in the system without going to drain, which is why the system is known as the recirculating gravity system.

B & V Water Treatment can offer advice on the water treatment regime required for your hot and cold gravity system with recirculation.

For more information or to arrange a site visit contact us.

Gravity System without Recirculation

A gravity system without recirculation is commonly found in residential properties and smaller industrial properties. A gravity system without recirculation is similar to a gravity system with recirculation, with the key difference being that the hot water is sent to drain via gravity rather than continually circulating until use. The benefit of this system in smaller properties is that water will only be heated just before use, which saves energy.

However, if there is a long pipe run between an outlet and the calorifier, temperatures may fall below 500C and lead to favourable conditions for microbiological contaminants such as legionella. To counteract this problem many systems use trace heating to ensure minimal heat loss along pipe runs. Trace heating uses thermostatically controlled electrical resistance tape covering the outside of the pipe before being covered in insulation foam to keep heat loss within pipe runs down to a minimum. Other actions such as flushing underused outlets, Pall filters or the incorporation of a water disinfection regime may be recommended.

B & V Water Treatment can offer advice on the water treatment regime required for your hot and cold gravity system without recirculation.

For more information or to arrange a site visit contact us today.

Pressurised Systems

In mains pressurised hot and cold water systems the mains water goes straight into a heat exchanger (calorifier, water heater or plate heat exchanger). As a result there is no need for a cold water storage tank. Protection against back flow is provided by a double non-return valve where the cold mains water enters the heater. The cold water runs straight from the mains to cold water outlets, where hot water may be recirculated from the heat exchanger. These systems are commonly found in houses with boilers and some small commercial office buildings.

As well as understanding the different types of hot and cold water system it is also vital to understand the key issues surrounding these systems.

The key issues within a hot and cold water system are:

scale on a shower head Scale

As with all systems that produce high temperatures, scale is a concern within hot and cold water systems. Scale can build-up within a calorifier especially in hard water areas and lead to the accumulation of calcium deposit at the bottom of a calorifier, making it harder for heat to transfer in the system. The problems caused by scale within hot and cold water can be greatly reduced by instilling an effective scale treatment regime.

corrosion within a hot and cold water systemCorrosion

Corrosion can be a concern within systems that are made-up of materials which are highly corrosive and can be treated with corrosion inhibitor chemicals. Corrosion in hot and cold water systems can reduce the lifespan of your system.



legionella on a pitri dish Legionella and microbiological contaminants

Legionella is normally the main microbiological concern when treating a hot and cold water system. The types of outlet that are typically attached to this type of system, such as taps and in particular showers, pose a significant legionella risk as they all release a water aerosol when used . Inhaling water aerosols is the only way humans can catch Legionnaires’ disease. As a result these systems account for a significant number of cases of Legionnaires’ disease. There are other microbiological contaminants you should also be aware of such as Pseudomonas, coliforms and e.coli. 


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