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Legionella prevention in Water Recycling

Legionella Risk in Water Recycling 

What is legionella?

Legionella is the name of the genus of bacteria that cause, among many others, the Legionosis infection and legionnaires’ disease, a severe pneumonia with a relatively high fatality rate. At least 50 species of Legionella have been described and twenty have been associated with disease in humans, but the predominant cause of legionnaires’ disease is L. pneumophila.

How is it spread?

Legionella spp. are opportunistic pathogens of humans and normally inhabit warm moist or aquatic environments where they grow in association with other organisms. In particular, they are known to grow in a range of protozoa. Their fondness for warm water means that they are capable of colonizing artificial water systems and equipment containing water. 

Legionnaires’ disease is not transmitted from person to person, but is of environmental origin and usually contracted by inhaling the organism in an aerosol produced from water contaminated with the organism. 

There is a chain of events leading to an individual becoming infected with legionnaires’ disease: 

  • the water system needs to become contaminated with the bacteria; 
  • conditions have to exist within the system for the amplification of the bacteria to sufficient concentrations to cause infection; 
  • the contaminated water usually needs to be dispersed into droplets fine enough to form an aerosol for transmission to the victim(s); 
  • inhalation of contaminated aerosols or, in rare cases, aspiration of contaminated drinking water; and 
  • the exposed individual has to be susceptible to succumb to infection. 

It is not a guarantee that a water system will become infected with Legionella, particularly if the turnover of water is high enough to prevent stagnation. However, if left for a period of 5-7 days, the water is highly likely to contain legionellae. 

Spa pools and hot tubs can expose many users and anyone in the immediate vicinity, while showers and taps are most likely to lead only to the exposure of individual users. Finally, for an individual to become infected following exposure they have to be susceptible, usually having predisposing conditions. Only a very small proportion of those exposed develop the disease, but increasing age, particularly 50 years and over, smoking, being male and being immunosuppressed through disease or treatment increases susceptibility.

The Legionella Risk Assessment

A risk assessment can be carried out to the following considerations:

  • Contamination – The chances of legionellae being introduced into the water or moist environment of the equipment/system are higher if the water entering is derived from a natural source, such as a river, lake or spring, or a private water supply, rather than a treated and disinfected mains water supply. 
  • Amplification – In order to grow, legionellae require nutrients and specific physical and chemical conditions. One of the most important elements of the environment is temperature. Legionellae can survive below 20°C but generally are not able to replicate.  They are considered to be capable of growth between 20°C and 45°C but rapid growth occurs between 32 and 42°C. 


  • Transmission – Legionella is transmitted via droplets in aerosolised water. Aspiration occurs when water is drunk but, instead of going down the throat into the stomach, goes down the wrong way into the lungs. Aerosols can also be produced by running a tap, flushing a toilet, water splashing onto hard surfaces or even small bubbles bursting on the surface of water 
  • Exposure –  The closer a person is to the source, the more likely they are to inhale the aerosol before it has become disseminated and the bacteria in it have died. This is what causes the high inherent risk in spa pools – the proximity of the water surface to the airways of the user allows for easy inhalation and aspirated. 
  • Host susceptibility – Some individuals are much more likely to become infected than others. Susceptibility increases with age, and males are more likely to become infected than females (ratio of 3:1). Smoking is a significant risk factor. Disease or therapy that reduces immunity, such as organ transplantation, cancer, blood disease and diabetes, also significantly increases the risk of infection.

Legionella risk in Greywater systems

Greywater is collected from hand wash basins/sinks, showers and baths which will therefore contain a lot of surfactants (soaps). These surfactants provide nutrients to bacteria and allow prolific growth. The temperature of the water, if between 20-45°C, also provides the perfect conditions for growth.

Despite the increased risk of Legionella being present in Greywater, the uses of Greywater generally do not create aerosols and therefore the risk of inhaling the contaminated water is minimal. If you were to use Greywater for irrigation, you would have to use drip-feed irrigation or would have to have a UV installed.

Legionella risk in Rainwater systems

Contamination: The rainwater, though pure when falling, can become contaminated by making contact with bacteria on the surface that the water is being collected from (an example of this could be bird excrement on the roof). 

Temperature: If the temperature of the water reaches 20°C or higher, the bacteria can grow. It is common during the summer months for roofs to reach temperatures upwards of 20 degrees so this is something to consider. This is a benefit of having a below-ground rainwater tank – they generally stay cooler and darker which also prevents growth of bacteria. 

Irrigation: If you’re planning on using rainwater for irrigation, it is important to consider what kind of irrigation you will be using e.g. either drip-feed or spray. Legionnaires disease is contracted through the aspiration of contaminated droplets so using a drip-feed irrigation system will pose less risk compared to spray or sprinklers. It is also worth reconsidering using a spray hose attachment for the same reason. If you decide to use a spray irrigation system or even a pressurised vehicle washing system (i.e. a pressure washer), then you will require the addition of a UV light which acts as a biocide, and kills any lurking bacteria.

Stagnation: It is also extremely important to note that if you are using your Rainwater harvesting system purely for irrigation purposes, you should not leave water to sit for any more than 7 days without draining/flushing the system and replenishing with new water. Stagnant water with no UV light will result in a contaminated water supply. However, if you are using rainwater for WC flushing, laundry and irrigation, the turnover of water will be much higher so stagnation is highly unlikely to occur. 

How is contamination prevented?

Having little or ideally no stagnation in any water tank will help prevent Legionella from materialising. This also goes for slow running water. Having one or more biocides e.g. UV light, bromine/chlorine tablets included in the system will help to sterilise the water before entering the tank or once inside.

 Legionella prevention in Aquaco’s systems

Aquaco’s systems have been developed by our in-house engineers using guidance British Standard 8580:2010 regarding Water Quality – Risk Assessments for Legionella control – Code of practice. 

If you place an order for one of our systems, we will recommend a system that is suitable for your requirements in terms of water turnover and capacity. Having a system that is disproportionate to the amount of water you will be using on a regular basis increases the risk of stagnation in your tank and therefore increases the chance of Legionellae being present. We can also supply additional equipment such as UV lights to help prevent your systems from being in contact with Legionella and bromine tablets to sterilise the water before it reaches the tank. 

Aquaco’s Managing Director James, specialises in Legionella risk assessment and is a City and Guilds accredited LCI Legionella Risk Assessor. You are in safe hands with Aquaco and can use our systems, safe in the knowledge that they have been designed with your health and safety in mind. 

Please contact us if you would like further advice or guidance on our systems. 

Rainwater Harvesting

Commercial Rainwater Harvesting Systems

What is Rainwater Harvesting (RWH)?

As a definition, rainwater harvesting is the capturing, filtering and storing of rainwater from the roof of a building, for reuse. However, it is more than just this. Rainwater harvesting is a method of ecological and sustainable rainwater management. The storing and reuse of harvested rainwater is an increasingly important alternative to the customary centralised drainage of rainwater.

On-site collection and use of rainwater covers a variety of applications including: 

  • toilet flushing
  • laundry
  • irrigation
  • climate control of buildings
  • cleaning

and more, at private and rented properties, residential areas, community developments, industrial sites, hotels, streets, parks, golf courses, theme parks, car parks, stadia, etc.

Rainwater Harvesting

There are many different types of rainwater harvesting system, designed to meet the different uses for the collected and stored water:

  1. Water collected in storage tank(s) and pumped directly to the points of use. These are most suited to reuse that requires a pressurised water supply. This includes spray irrigation systems, vehicle washing systems, washing machines etc.
  2. Water collected in storage tank(s) and fed by gravity to the points of use. These are most suited to small water butts, with a tap at the base. In rare cases, they can be very effective in properties with high eaves, or roof plant-rooms where the main collection area sits above the plant area. In these cases the whole system can be fully gravity fed.
  3. Water collected in storage tank(s), pumped to an elevated cistern and fed by gravity to the points of use. These are most suited to supply critical points of use i.e. WC flushing. The reason for this is that, as a WRAS fluid category 5 liquid, any mains top-up must be accompanied by a type AA or Type AB air gap. In the event of a power outage, any pumped systems will fail. However a gravity fed system will continue to provide water, and top-up with mains water via a mechanical ball valve, offering a robust supply of water.

How do you collect rainwater in the UK?

Rainwater is harvested from roofs (via guttering) or hardstandings and contained in a tank, either above ground or below ground. 

Hard roof surfaces are considered the most suitable for rainwater collection. Guttering and pipework should allow the water to freeflow from the collection surface to the storage tank by gravity or siphonic action. Before entering the tank, the water is filtered to separate any debris such as leaves and moss from the water. If possible, it is recommended to avoid collection from green roofs, and from trafficked areas. This is because green roofs can discolour the rainwater yellow through nutrient leaching.  Trafficked areas also require the addition of a hydrocarbon interceptor to remove fuels and oils form the rainwater prior to use.

Systems and treated water should conform to the British Standards. The most common standard used is the British Standard BS8515:2009, however this was superseded in 2018 by the new standard BS EN16941-1:2018. All systems should conform to this standard. 

Water that conforms to Table NA.3 of BS EN16941-1:2018 (below) will provide water suitable for WC flushing, laundry and garden watering in most residential commercial and industrial situations. Additional equipment such as a UV (ultraviolet) light or chemical disinfectants can be used to further sterilise the water. 

Rainwater Harvesting

Is RWH legal in the UK?

Yes, it is perfectly legal to harvest rainwater that falls onto your property in the UK. In fact it is often encouraged. As the demand on water increases due to an increased population and erratic, less predictable weather conditions, harvesting your rainwater which would otherwise soak away, will reduce the demand on your mains water supply, and help to attenuate surface run-off aiding in the prevention of localised flooding. It will therefore save you money on your water bill and also reduce your carbon footprint. 

It should be noted that if you live in an apartment or terraced property you may need to ask permission of the free-holder, or neighbour if the roof and downpipes are shared. However, this is often just a formality!

Finally, there are also British Standards and other regulations, such as building regulations, that must be followed so be sure to check these before installing a system. 

What are the benefits or RWH?

There are lots of reasons to harvest your own rainwater. A few are listed below:

  • Less calcium build-up in domestic appliances such as washing machines
  • Less demand on mains water
  • Cheaper water bills 
  • Makes your home more sustainable
  • Attenuation of surface run-off (Sustainable Urban Drainage Systems)
  • Improved self-sufficiency, and carbon footprint reduction.

Is Rainwater harvesting worth the money?

Absolutely! If you choose to invest in a RWH system, you will be futureproofing your home against water shortages, water price increases and will be reducing your carbon footprint.

Rainwater is considerably better for watering your plants and the general health of your garden than mains water because it doesn’t include the chemicals that are used to treat the mains supply.

If used for laundry, you may find you won’t need to use as much softener and your washing machine will likely last longer because it won’t get clogged with limescale. 

Rainwater Harvesting

What are the best Rainwater Harvesting systems in the UK? We're glad you asked!

Here at Aquaco, we are at the forefront of research and development of water recycling technologies.

We have an in-house team of engineers who are driving the industry forward by constantly designing and testing new processes, materials and technology in order to provide the most efficient, cost effective solution for your home or business.

If you’re thinking about investing in a Rainwater Harvesting system, then please fill out the ‘Get a Quote‘ form, and one of the team will contact you with further information. Otherwise, you can call us on 01622870200. 

Rainwater Harvesting