Drinking water quality and bacteria in water distribution systems (Part 1)

Drinking water quality is something we take for granted in the UK but it is still the preoccupation of Water Safety Group team members, microbiologists, site facility managers and water hygiene technicians. We now understand the greatest risk to human health is from waterborne pathogens, viruses and infections existing largely between water entering our buildings and the building water distribution system in it, as well as the last few metres before point of delivery. So how are microbes and pathogens in our water distribution systems best managed?

Water distribution – before it reaches our buildings

Water passes from rivers, reservoirs and lakes into public treatment facilities where chlorine is introduced to cleaned water which is then filtered. Additives are introduced before the water is stored. From here, it is distributed to hospitals, houses, schools, commercial and industrial buildings and so-on. At this point, water is usually fresh, clean and safe. However, it is far from contaminant-free.

Bacteria in water, algae, invertebrates and viruses

The entire water distribution system – reservoir, well, pipe, storage tank and so-on are natural homes to multiple species of bacteria, algae, invertebrates and viruses. Perfectly safe water contains millions of non-pathogenic microbes in every glassful. The same is true of bottled water. Some contaminants are harmless or even good for human health. Some microbial communities might actually protect pipes from chemical and physical stress. Understanding the role of microbes helps us better select suitable materials for pipework and ensure water distribution systems from point of supply (ie. mains-water or private borehole) to point of delivery (ie tap / sentinel, shower, spray nozzle, feed-water tank etc), are protected and remain healthy.

The microbes in our water distribution system

Some microbes live perfectly naturally and are long-term inhabitants of water distribution systems but only cause illness to humans in certain conditions. Positive results for particular microbes, such as Escherichia coli (E. coli), are an indicator that pathogenic microorganisms may have entered the water distribution system. A common characteristic of microbiological communities in water distribution systems is their propensity to form biofilms. Some are described as planktonic (they float freely in water), whilst others attach themselves to surfaces by secreting sticky polymers made of DNA, proteins and complex carbohydrates. These can become highly attractive host environments for opportunistic pathogens that disinfectants sometimes struggle to overcome.

Whilst many pathogens are microbes that live perfectly normally in water distribution systems, and can remain totally or relatively harmless to human health, some people are more susceptible to ill-health and underlying water system conditions can exist that lead to infection incidents – with some opportunistic pathogens found particularly within water distribution systems. These include for
example:

Non-tuberculous mycobacteria (NTMs) such as Mycobacteria avium, M. intracellulare, M. kansasii and M. fortuitum. These organisms can cause serious pulmonary and lymphatic disease, skin ulcerations and other health issues.

Legionella pneumophila is the causative agent of Legionnaires’ disease (pneumonia) and milder variation Pontiac fever. In the UK during the 12-months to 31 December 2018, a total of 814 Legionella pneumophila cased were reported / notified (Public Health England).

Pseudomonas aeruginosa can occur in water distribution systems within buildings and can infect ears, skin, eyes and in some cases, cause pulmonary disease. This opportunistic pathogen is the preoccupation of Patient and Water Safety Boards in hospitals up and down the UK and is extensively and continuously tested for in hospitals, care homes and buildings with particularly vulnerable inhabitants. Water is the source of infection.

Escherichi Coli (E. Coli) can cause nausea, vomiting, abdominal pain and diarrhoea if consumed in contaminated water.

Campylobacter Jejuni can be found in contaminated drinking water and cause infections with symptoms of cramping, diarrhoea, fever and pain.

Hepatitis A is an infection and can be present in drinking water. Symptoms include dark urine, jaundice and stomach pain.

Giardia Lamblia is a waterborne parasite that causes nausea, cramps, gas and diarrhoea.

Salmonella is a common pathogen that can cause chills, fever, headaches, diarrhoea and is infected through water and food ingestion.

Cryptosporidium is a parasite that spreads through contaminated drinking water. It can cause severe pain and painful diarrhoea.

These and other infectious microorganisms contaminate drinking water and can cause ill-health in humans, especially in children and vulnerable people with weak or impaired immune systems. Infectious microbes may be present in human and animal waste. Wells and other water sources can become infected by storm or drain water run-off from roadways, farms, discharges from sewage treatment plants or septic system discharges or water systems with poor water quality or bacteria control or systems where water purification and disinfection is not robust or reliable over a period of time.

As inhabitants for microbes, biofilms can contain many times more bacteria cells than the water flowing through the pipes in your domestic water system. They can also act as reservoirs within which both bacterial and viral pathogens can thrive. Bacteria can also live within amoebae and other parasites that can live in water distribution systems. In aquatic ecosystems, amoebae are predators that eat bacteria. However, some bacteria including pathogens like Legionella pneumophila and Mycobactererium avium, can resist digestion and actually grow and multiply within biofilms,

Many biofilms in water distribution systems pose no significant threat to human health but they can still cause physical damage such as corrosion of pipes and blocking intake valves. They can also break down chemicals used to minimise microbial growth, while others may release nutrients that help sustain pathogens in water distribution systems.

Common water treatment strategies therefore often target biofilm formation without sometimes fully understanding what microbes may exist within your own water distribution system. The use of chlorine for example to kill pathogens may not reliably prevent opportunistic pathogens such as Mycobacterium avium which is more resistant to chlorine. Some disinfectants also have unfortunate by-products that become nutrient sources for opportunistic pathogens in water distribution systems. For example, chloramine is a by-product produced by some disinfectant treatments but chloramine can also encourage the growth of certain nitrifying bacteria within biofilms that remove the disinfectant residual.

It is important for building managers and Duty Holders to understand the water microbiology occurring within your own water distribution system. They need to continually monitor water chemistry, microbiology and bacteria in water. From here, building managers and Duty Holders can, if necessary, more reliably select appropriate methods of disinfection, secondary disinfection and protect 
water and human health.

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Alex Winter

Alex Winter

Alex is a Marketing Contributor and has 5+ years in water treatment and ACoP L8 compliance and works across all six linked areas of the business; Water Treatment, Waste Water, Water Hygiene, Air Hygiene, Engineering and Legionella Training.

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