The Drinking Water Inspectorate (DWI) reported that UK water companies reached 99.92% compliance with European drinking water standards over the past 12 months.
While the UK is rightly credited with having very high-quality tap water, on rare occasions pathogens have leached into the drinking water supply. For example, the DWI’s 2007/08 report states that many water companies have had to cope with treated water being contaminated by flood water in the past 18 months. An outbreak of cryptosporidiosis in southeast Hampshire in 2005 was monitored by the Health Protection Agency and was found to be caused by seasonal fluctuation in local river levels and supply, which led to oocysts infecting the drinking water supply.
Water treatment companies have to undertake regular tests to ensure that there’s no more than one cryptosporidium spore per 10 litres of treated water, because disease has been shown to break out when levels exceed this concentration.
The ‘boil water’ alert issued by Anglian Water in June 2008 caused disruption to a number of Northamptonshire businesses after cryptosporidium was detected in the water supply. The infection was traced to a single rabbit that had entered the Pitsford water treatment works.
Its droppings contaminated the drinking water with crytosporidium spores and alerted businesses had to flush out 1,000 miles of pipework and disinfect the plant using ultraviolet light. This article will look at how ultraviolet light can be used within buildings to help keep mains water safe in the event of similar outbreaks.
Cryptosporidium spores, or ‘oocysts’, are microscopic and carried in the faeces of humans and animals. Infection is caused by drinking water contaminated with the spores, and symptoms include diarrhoea, vomiting and stomach cramps. Because they’re so tiny, spores are not trapped by normal filtration processes and are resistant to disinfection using chlorine. However, they can be rendered harmless through boiling or freezing the water, and through ultraviolet light treatment.
The water disinfection properties of ultraviolet light were discovered more than 100 years ago. Ultraviolet light (UVC) protects against infection because it damages the DNA of microorganisms so that they can’t reproduce.
Ultraviolet light is used to describe the part of electromagnetic spectrum between visible light and X rays. There are three ranges of ultraviolet light:
Different organisms require different doses of UVC light to inactivate their DNA. The cyst-based parasite cryptosporidium parvum has been shown to be inactivated by a UV dosage of 7.9 microjoules per square centimetre (mj/cm2). E. coli requires 5.6mj/cm2. Treating drinking water with UVC light for a duration of one second will be sufficient to destroy the DNA of 99.9% of pathogenic organisms. This is the same time it takes to press the button to dispense the water into your cup.
As a supplier of mains-fed water machines to schools and hospitals, and an approved supplier to the NHS Purchasing and Supply Agency, we have to ensure that our water machines have filters that block anything larger than 0.5 microns (eg the gaps in the granular activated carbon filter are too small for cryptosporidium spores to pass through).
As an additional safety precaution, we include an ultraviolet bulb in our machines. So each time you press the dispense button, the water in the tank is zapped with the ultraviolet rays, killing any microorganisms that may be present.
Tana Water was one of the first water dispenser manufacturers to take advantage of UV light technology. Our water machines have a built-in safety mechanism to prevent them from dispensing if the ultraviolet bulb stops working before its mandatory six-monthly service by our engineers.
Each machine also has a central processing unit linked to a Compaq Ipaq handheld computer, so that engineers can monitor the amount of water that has been dispensed and assess whether a service needs to be brought forward, to ensure optimal efficiency of the filter and UV bulb.
By combining chlorine filters and 11 Watt ultraviolet light bulbs in our water machines, we prevent bacteria from reproducing in the water once its protective chlorine has been removed, so your water tastes great and you have the peace of mind that it’s germ-free.
The first and second stages of filtering use activated carbon to remove physical and chemical contaminants including chlorine, limescale, rust, cysts and volatile organic compounds. The third stage involves the UV treatment of pathogenic microorganisms.
UV light filters in water machines have the benefit of being able to kill 99.9% of water-borne and airborne pathogens without adding any chemicals to the water. By pre-filtering with carbon, any cloudiness or ‘turbidity’ is removed from the water to ensure that the ultraviolet lamp can operate at optimum efficiency.
At Tana, we’ve worked with the European Point of Use Drinking Water Association (EPDWA) to assess how water dispensers could potentially become agents of cross-infection from airborne pathogens such as Haemophilus influenzae, the bacteria that cause influenza.
In risk areas such schools, colleges and hospitals, where large numbers of people are using the same water machines, it’s important that coughs and sneezes don’t contaminate the drinking water in water coolers. As a result, we introduced ‘zero air gap’ technology into our machines. This means that the water dispensed comes straight from the mains into the sealed carbon and UV filtering chambers and never comes into contact with the surrounding air until it’s in the cup that you’re drinking from. This removes the risk of surrounding air mixing with water from which the chlorine has been removed.
After more than a decade of supplying mains-fed water machines to hospitals, care homes, hotels, schools, factories and government offices, we have incorporated infection control into our product design.
As a result, we have assessed the potential risk from storing water that has had chlorine removed to improve palatability, but then stands at room temperature for a period of time before being consumed. By combining 0.5 micron carbon filters and ultraviolet light bulbs in our water machines, we prevent bacterial contamination of water after the chlorine has been filtered out. This improves the taste while maintaining the safety of the water, even in the event of a ‘boil water’ alert.
Nick Heane is the managing director of Tana Water (UK), a wholly owned subsidiary of Tana Industries, one of the world’s leading developers and producers of mains-fed water dispensers.
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