Ultraviolet sterilisers use ultraviolet (UV) light to kill bacteria and micro-organisms in water that passes through the system. Though not generally required on UK mains water, there are more than half a million people in the UK whose only source of drinking water is from a private water supply such as a well, stream or borehole. Water from a source such as this is unlikely to be micro-biologically safe so a UV system may be employed to obtain bacteria free drinking water from a private, non-mains water supply.
There are a wide variety of ultraviolet systems on the market, from small, low cost, low wattage systems with plastic housings to large stainless steel units. Where very high capacities are required the larger systems are available by special order or off the peg systems can be connected in sequence or in parallel.
This page sets out to explain what a UV system is, when you should consider using one and what to consider before purchasing one.
What is an ultraviolet steriliser?
It’s long been known that sunlight is a natural disinfectant and this is because light in the ultraviolet spectrum alters the genetic material (DNA) inside bacteria, viruses and other micro-organisms leaving them unable to replicate, thereby effectively killing them.
A UV system replicates this by (very basically) running water through a tube with a specially designed UV light in it. As UV light disinfects instantly, a UV system works ‘on demand’ with no contact or storage tanks required.
What does an ultraviolet steriliser do?
Fitting a UV system can make water from an untreated water supply biologically safe to drink by killing micro-organisms and destroying bacteria, viruses, protozoa and oocysts (parasites) including but not limited to:
- E. Coli
- Clostridium perfringens
- Coliform bacteria
Although different viruses and bacillus require differing doses of UV light to render them inactive, the lamps used inside UV systems are especially designed to produce light at the wavelength most lethal to micro-organisms (which is 253.7nm for the science geeks amongst us) making these systems one of the most effective ways to kill disease-causing microbes.
Most UV sterilisers have the same basic layout with a control box and a UV chamber containing UV lamp inside a transparent quartz sleeve. The UV chamber has an inlet and an outlet to allow water to pass through it.
Why use an ultraviolet steriliser and what are the advantages?
Ultraviolet light is highly effective against almost all bacteria and micro-organisms and unlike chemical disinfection, nothing is added to the water so there are no harmful by-products.
The system is designed to keep working day and night and UV lamps are made to be kept on 24 hours a day: in fact, switching them on and off can reduce lamp lifespan. Despite this, UV lamps are very efficient and systems only use a small amount of electricity.
UV systems require only minimal maintenance. A 6 monthly service to replace the UV lamp and clean the quartz sleeve is usually all that’s needed, though the quartz sleeve may require cleaning more often if the water supply is very hard water and / or contains high levels of iron or manganese.
Ultraviolet Steriliser Advantages
- Highly effective against bacteria and micro-organisms
- Keeps working 24/7
- Minimal maintenance required
- UV light disinfects instantly
- No storage tank required
It’s worth bearing in mind that there are a couple of disadvantages as well, and these should be considered before purchasing a UV steriliser.
UV sterilisers don’t remove particulate or chemicals / heavy metals. As supplies containing bacteria usually also contain particulate, additional filtration that incorporates a sediment reduction element is recommended.
This is particularly important as any particles or turbidity in the water potentially give bacteria something to hide behind and will prevent them receiving the full dose of UV. As such, it is recommended that the water is filtered first to make sure it is completely clear and that any micro-organisms are fully exposed to the UV light. We recommend a 5 micron sediment pre-filter should be installed upstream of every UV steriliser installation.
You should also bear in mind that UV does not change or improve the taste, odour, colour or dissolved solid content and that further filtration / treatment may be necessary. Finally, it should be noted that UV offers no residual protection so treated water should not be stored for long periods.
What types / sizes of ultraviolet steriliser are available?
There are a variety of different sizes available and we supply systems ranging from the 6 watt ACUV62P, generally used for low volume water cooler applications, through to the 55 watt ACUV554D with a flow rate of up to 51 litres a minute which is suitable for treating the incoming mains water supply for a small hotel / B&B.
Selecting the right ultraviolet steriliser
To work our which system to purchase, you’ll need to know roughly what maximum flow rate you require in litres per minute. Generally we find that a 30 watt UV system is suitable for an average size house with one kitchen and one bathroom but certain factors such as hosepipe usage can affect this dramatically and we would always recommend contacting us for free advice before making a purchase.
Sizing a UV for a mains supply is relatively straight forward as the water has already been treated once. However, if you are treating water from a private supply, the water chemistry will need examining in more detail before determining whether UV sterilisation is the right solution. You can obtain a water analysis by contacting the environmental department of your local council, employing a specialist contractor (most local councils which have private water supplies in their jurisdiction will have a list of private water supply contractors) or identifying a local laboratory to send a sample to.
Which supplier should I choose for my ultraviolet steriliser?
Aqua Cure are proud of our many years in the water treatment business and consider ourselves water purity experts. Our exhaustive experience with ultraviolet sterilisers and lack of ties to a single manufacturer means that we can offer impartial advice on the ideal system, size and wattage for your requirement.
As well as a wide range of UV sterilisers, we also stock the necessary 5 micron sediment filters and associated housings you’ll need to pair your UV with to ensure optimum sterilisation. To the uninitiated, trying to navigate the various options available for pre-filtration, as well as the different specifications of UV steriliser can seem daunting. If you need some guidance, please feel free to call the experts for some no obligation advice.