Warm Water Disinfection - handy hints and mis-directions!
What is a warm water system?
This question is a bit of a controversy in Australia. Definitions change between jurisdictions, along with management requirements! The definition may include a system supplying warm water from a central point - or a hot water service with multiple TMV's or a system where the bulk of the system volume is warm Refer to SAI global for more info).
'Warm' may be anything less than 60C or less than 45C depending on where you live. Confusing eh? The first step is to know your local regulatory framework. This should be clearly identified in your Water Safety Plan. If not it's time to do some investigating and work out exactly what is the nature of the beast you own! Or better still - get some Risk Management sorted out!
Beware! even if you discover your system is Hot (in a good way!) and not covered by the Legionella regulations. You still have a duty of care (and other legal imperatives) that might come back and bite you on the bum!
The Triangle of Trouble
All we really want is to have a shower safely! This is my own way of trying to explain the competing considerations we face. So we'll start at the top and work clockwise!
Hot Water
If you supply hot water then you have a scalding risk - and anyway in Australia must comply with the regulations regarding temperature at outlets; so you need TMV's.
On the other hand, if you have a hot water loop then you can assume some level of disinfection from the water temperature. The downside is any disinfectant that came in with the mains supply is probably lost.
Any disinfectant that you choose to add to this system must be able to cope with the temperature without causing corrosion / disinfection by-product issues.
The cold water (it is probably not that cold - anything over 20 Celsius is not cold) is not addressed and contamination at TMV's is highly likely. Watch out because cold water above 20 Celsius makes your TMV use less hot water to meet the target delivery temperature creating stagnation on the hot side!.
Warm Water
If you supply warm water there is no scalding risk. However, temperatures are ripe for bacteria to grow and the Legionella risk goes up. Keeping warm water 'warm' is then a hydraulic issue. Can you guarantee the temperature of the water when it leaves the plant is the same at the tap? Your site assessment and risk management plan should tell you.
Some form of disinfection to make up for the temperature drop, at least periodically, is needed. Most warm water systems use centralised TMVs anyway. So the TMV issue remains.
The issues with not-so-cold water still remain.
So whether you have a hot water system or a warm water system, by any definition, you are still faced with significant amounts of warm water to manage.
Disinfection
Disinfection in any application is always the last resort. If you can't reliably control it by any other way - kill it! This is the last level of the Hierarchy of Control. If your Water Safety Plan tells you you are running a high risk facility - it probably also tells you that some sort of disinfection is a very good idea.
Disinfection needs some consideration. In the process of selecting a disinfection method you'll need to look hard at your system and do some 'leg work'. What are the problems associated with a) hot water? b) warm water? c) cold water? and you're disinfection plan. A reality check will tell you that nothing you select will be perfect. There are a whole heap of things up the Hierarchy of Control that will determine the success of your disinfection process.
So if you have a problem disinfection by itself is unlikely to fix it!
Misdirections
There are a number of urban myths on warm water disinfection. Sadly many of them are still active and actively applied. So here we go on some myth-busting!
Myth 1. Cold water is not an issue / hot water is not an issue - I only need to address the warm water:
Read the facts pals! Cold water is generally NOT cold, especially if it has sat inside your building for 24 hours before you use it. If cold water is not an issue why have people died from disease from ice machines and chilled drinking water fountains. After all they were supplied solely by cold water?
In some jurisdictions in Australia more cases of disease are attributable to hot water supplies than cold and warm combined. Published data shows Legionella surviving at 60 Celsius and above for significant periods.
Myth 2. An ultra violet disinfection on a warm water system is a good idea:
Many warm water systems come fitted with a UV disinfection unit. I have no idea why - because they are a bad idea! There are three reasons why I can say that:
UV only works on water passing through the unit. It does not affect biofilm. It does not have any residual effect. It will not reach outlets where people get exposed.
UV light deactivates chlorine and monochloramine the two most common disinfectants in your mains water supply. It effectively knocks out any residual effect you might have coming in to the system.
UV systems have a by-pass on them so they can be isolated for servicing. Unless regularly flushed this is a built dead leg.
Myth 3. I have a disinfection system so the problem is sorted
Well clearly from Myth 2 above this is not the case! If you have arrived at the above conclusion you don't understand the Hierarchy of Control. Any disinfection method will fail if the system it serves is not optimal. Your risk management plan, design and maintenance are the things that will make or break your disinfection method.
Handy Hints
I did mention handy hints in the blog title so here's a short list:
Get a risk management plan, water safety plan, water safety risk management plan - whatever you want to call it
The less complexity you have in your system the easier it is to manage. If you don't need it or don't use it remove it.
Remove your UV warm water disinfection system. Let your system inform your choice of disinfection.
Set target temperatures for hot, warm and cold and check them regularly.
All of the mentioned areas above are what we specialize in, our business delivers industry leading processes, systems, training and support as well as market leading disinfection products that will enable you to manage and reduce risk of waterborne infection. We are an ISO accredited business and hold Systems, Safety and Environmental certification, please feel free to contact us if you would like to talk more.
More Info.
Australian Government 2015. EnHealth Guidelines for Legionella Control. https://www1.health.gov.au/internet/main/publishing.nsf/content/A12B57E41EC9F326CA257BF0001F9E7D/$File/Guidelines-Legionella-control.pdf
Water Supply Code of Australia 2011. https://www.dropbox.com/home/Built%20Water%20team%20folder/Library/11%20Water%20Supply%20Code%20of%20Australia%20Versions%203.1?preview=Water+Supply+Code+Version+3.1.pdf
UK HSE 2013. Legionnaires’ disease The control of legionella bacteria in water systems
US EPA 2016. Technologies for Legionella Control in Premise Plumbing Systems: Scientific Literature Review https://www.epa.gov/sites/production/files/2016-09/documents/legionella_document_master_september_2016_final.pdf
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