Building Hot, Warm & Cold Water Systems Stagnation

Within Warm Water systems it is a requirement of the enHealth Legionella Guidelines, SA Legionella Guidelines and other guidelines and standards across Australia to routinely flush distal and infrequently used outlets weekly within high risk premises, but in cold and hot water systems generally there is a lack of requirement to flush these and can be just as much risk as a warm water system.

Another thing we get asked is can we describe what a dead-leg really is. The issue is that there are really two types and we need to start talking about them both. Can it be flushed or water discharged from it or not? The best way we can differentiate between the two of them is:

Dead-Leg - this may be a tap or outlet that can be easily flushed by turning on a tap or isolation valve but is infrequently used.

Blind-End - this is pipework that is capped or welded shut so that it cannot be flushed.

If a water system is left to stagnate within either of these biofilm and bacteria will grow, and quickly in the right conditions. Blind-ends act as seed lines for bacteria to reinfect treated systems - if you cannot flush it there is no chance of introducing a disinfection treatment to it.

Two jobs that we have worked on in the last few months really showed how important it is, not only within existing buildings but also within buildings under construction.

Quick Overview Case 1.

Existing site where many separate buildings exist, the whole site is being re-developed, some of the buildings are being retained - others demolished.

Whole of site System Stagnation for three to four weeks:

This type of discharge was systemic across the site from the cold water supply, and circulated hot water supply , hydraulic deficiencies were found within all unused buildings.

This site whilst operational had clean water discharging from the outlets, the stagnation period allowed for the proliferation of biofilm and potentially system corrosion.

Quick Overview Case 2.

New multi Story building, site in construction for three years.

Water samples taken on the same day and sent to a NATA accredited laboratory for testing.

Heterotrophic Colony Count (HCC) Total Plate Count (TPC) testing across all floors and the storage tanks feeding the system.

RESULT - HCC

1,300 cfu/mL
1,400 cfu/mL
160,000 cfu/mL
130,000 cfu/mL
190,000 cfu/mL
340,000 cfu/mL
600,000 cfu/mL
47,000 cfu/mL
46,000 cfu/mL
2,800 cfu/mL
41,000 cfu/mL
170,000 cfu/mL
520,000 cfu/mL
430,000 cfu/mL
27,000 cfu/mL
550,000 cfu/mL
140,000 cfu/mL
470,000 cfu/mL
100 cfu/mL (Storage Tank 1)
<100 cfu/mL (Storage Tank 2)
70,000 cfu/mL
160,000 cfu/mL

This systems hydraulic services installation is flawless, Inspection Test Plans (ITP's) for all installations, short runs to outlets and in copper pipe, all aerators removed when tapware was installed and flushed on commissioning.

Note - with high HCC / TPC results like these the likelihood of Legionella being detected within everything else growing would be very difficult, in this case all samples came back <10 cfu/mL for Legionella within the first phase of testing. While there is no clear relationship that exists between HCC and a public health risk or the presence of Legionella it can be used as an indicator of system cleanliness. Once the first decontamination took place and the HCC levels reduced Legionella was detected in the system.

Questions we need to ask:

This building in its construction phase from in-ground to completion is no different to any other multi story building being built. So why the high level of HCC / TPC? - in other buildings it could be for a few reasons depending on the building hydraulics and its construction processes but in this case the most likely cause is system stagnation.
Remember in buildings that have Cooling Towers the potable water is piped into them and can seed these towers - the evidence of Legionella outbreaks in cooling towers predominately precedes multiple days of high temperatures reducing the biocide effectiveness, seeding an already under stress cooling tower during these types of conditions increase the likelihood of bacterial growth, would we rather not have these levels of HCC entering them?
Are other buildings testing for bacteria and HCC / TPC to determine system cleanliness? in this particular example the Hydraulic consultant who created the scope knows the significance of bacterial infection in building potable water systems so specified that HCC and Legionella samples were to be taken, are all hydraulic consultants this aware of the issues and ensure that their clients are protected?

FOR THOSE READING THIS THAT DO NOT OWN OR MANAGE A TYPICAL HIGH RISK FACILITY.

We would like to share some advice for home owners and hotel owners.

For Hotels:

At one point in time you will have someone visit your premises that may be immune compromised such as having cancer treatments or taking drugs that lower the immune system.

If you are leaving outlets stagnant.
If you are not servicing your thermostatic mixing valves and tempering valves.
If you are not ensuring that your hydraulic systems are operating within the required parameters.
If you are not carrying out weekly flushing of distal and infrequently used outlets.
Or not maintaining your hydraulic services and assets such as filters, ice machines, chilled water units, spas and pools etc.

You are potentially putting yourself and your clients at risk. A health risk management plan can be put in place to greatly minimise the potential from contracting a bacterial infection and or scalding.

For home owners:

If you have anyone in your family or someone visiting that are immune compromised they are potentially at risk of contracting waterborne bacteria from your home if your system is colonised

A few tips:

If you have all directional shower roses push them down against the wall and allow them to drain after use.
If you have flexible shower hoses after use hang them so that they can drain but not touch the floor.
If you have en-suites or other bathrooms that do not get used often run the tapware for a few minutes every week at full flow making sure that you do not allow the water to become airborne, switch on the fan and wrap a cloth around shower heads etc. or just make a point to use them at least once per week.
Have a licenced plumber inspect your hot water service and tempering valve for correct operation.
If you have spa baths ensure that they are cleaned with a suitable cleaning agent and free from dirt and build-up.
Decorative fountains should be cleaned regularly.
Avoid the use of in home ice machines.
Replace any filtration devices and have them treated with biocide.
Seek advice on your home water system - if anything take a water sample from showers, basins and filters then send to a NATA accredited Laboratory for Legionella testing before they come home after treatment, if you have an issue there are ways of dealing with Legionella reasonably cost effectively at point of use.