Stagnant water advice for reopening businesses

Where a building has been vacated for a period longer than one week, or water usage has significantly reduced; we recommend you seek expert advice to establish a scheme of control and/or water safety plan to manage the water hygiene which is tailored to your water system. This will help you avoid running into water quality issues and a costly recovery you can also find guidance on recovering drinking water supplies in buildings.

We need to close our building or we aren’t going to be using as much water.

What should we do to keep the water safe?
When a water system isn’t being used enough, water stagnation is likely to occur. This provides perfect conditions for a harmful bacteria called Legionella to quickly multiply and colonise your water system. The Legionella Code of Practice gives detailed guidance on managing the risks.
So what can you do? 
Scenario 1 – I can still visit my premises during the pandemic
If you can still visit the premises to keep it secure, etc., then take that opportunity to simulate normal water usage. Get into a weekly routine of flushing all of the outlets and then checking temperatures at random hot and cold outlets, ensuring cold is below 20°c and hot above 50°c throughout the premises. It will be necessary to keep records of these actions – keep a log of all rooms and outlets and then add records of all water temperatures and that flushing has taken place.
Simple flushing and temperature checks can be easily established and will get you by for a short while. But you should also talk to a Water Safety Professional who can easily help you come up with a scheme of control tailored for your premises. Note: If you cannot achieve cold below 20°c and hot above 50°c, the control scheme is not working – you need to seek professional advice quickly.
Scenario 2 – I won’t be able to visit my premises during the pandemic
If the premises can’t be attended during the pandemic, then you need to think about de-commissioning your water system.
Some things to consider:
  • Smaller water heaters – turn the electric supply to all water heaters off and allow them to cool down (you could flush all the hot water away to speed this up)
  • Larger water heaters (usually in plant rooms) – check with your maintenance team to see if you can isolate water and energy supplies, allow these to cool and drain down
  • Check with you maintenance team if it is possible to turn off and isolate heating systems without causing other problems
  • Cold weather and freezing pipes – you could drain down the water systems (if a pipe doesn’t have water inside it can’t freeze and burst while you aren’t there)
  • Remove shower heads and flexible hoses and make sure these facilities can’t be re-used until the system is properly re-commissioned
  • Cooling towers – if you have these and they are to be turned on/off, you will need to notify your local authority (seek advice of a Water Safety Professional)
  • Consider using this downtime to coordinate a Legionella Risk Assessment prior to recommissioning the site
This likely to include flushing / descaling / cleaning / disinfection / sampling and will not be a quick process. Also, it’s likely that the demands on Water Safety Experts are going to be high so plan for delayed re-opening. Speak to a Water Safety Professional now and give them time to review your premises and ask that they provide a commissioning plan for you.

What can happen to my water system?

Water that has been held in your water tank or water pipes for any longer than 24 hours will deteriorate and will become stagnant due to loss of chlorine residual, warming and interaction with the plumbing system materials. When stagnation occurs within the system it can allow bacteriological growth, most commonly this can lead to legionella colonisation but can also cause taste and odours, discolouration and an increase in the levels of dissolved metals. If this has happens and you attempt to use the water system as normal then you could expose yourself and others to legionella or other microbes, potentially harmful levels of contaminants or foul and smelling tasting water.

What should I do if the water has an unusual taste, odour or appearance?

Systems should be flushed by opening each outlet for at least two minutes, for outlets connected directly to the mains this should result in the water temperature dropping as water from the underground water main passing to the tap. When flushing outlets spray should be minimised to reduce Legionella risk. Tank fed pipework should be flushed after the tank has been drained down.

If the problem persists after flushing and cleaning then please contact us.

How do I ensure that I do not expose users to high levels of metals of other contaminants from the plumbing system?

Systems should be flushed by opening each outlet for at least two minutes, for outlets connected directly to the mains this should result in the water temperature dropping as water from the underground water main passing to the tap. When flushing outlets spray should be minimised to reduce Legionella risk. Tank fed pipework should be flushed after the tank has been drained down. Please view the guide for more information.

Where can I find advice on managing my water system and Legionella control?

BSEN 806-5 Specification for installations inside buildings conveying water for human consumption – operation and maintenance. This standard provides specific requirements for the operation and maintenance of installations inside buildings. Section 6 of this document provides details on operation, section 12 provides details on maintenance, Annex A provides details on frequency for inspection and maintenance and Annex B provides details on inspection and maintenance procedures.

BS 8558 Guide to the design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages.

Guidance on BSEN 806. This standard provides additional guidance on best practice and section 6 provides details on water quality checks for stored water.

Legionella Code of Practice is freely available along with information on water safety plans for buildings.

Why do I need to manage legionella?

If you are an employer you will have a duty of care to your employees and anyone visiting your premises and the management of your water system falls under the COSSH Regulations and Health Safety at Work Act.

We had to vacate our building quickly and had no time to set up a scheme of control or drain the system down?

You should be cautious and seek professional advice on re-commissioning your water system. You can find a water hygiene expert.

How much will it cost to recommission my water system?

This all depends on the size and complexity of your buildings water system and whether any parts of the system have been in use. It's always best to get expert advice specifically for your water system but to give an idea of what's involved:

  • A small water system which perhaps just has a male and female toilet and kitchen with a simple combination boiler providing hot water may require just a thorough and safe flush of all parts of the water system and cleaning and descaling of outlets.
  • A larger building may have cold water tanks, more complex hot water plant and water recirculating systems. These more complex buildings will require a risk assessment and a recovery scheme of control prescribed by an expert.

So what sort of water systems and fittings pose a risk?

Certain things on water systems pose risks and require routine checks and maintenance. Water tanks, hot water storage vessels, hot water circulating systems, showers, thermostatic mixer taps and valves, expansion vessel and the design of the water system and pipework itself. The HSE guidance helps explain what you need to do.

Should I arrange for a Legionella Risk Assessment?

Where the water system is quite complex it’s a good idea to seek expert help to identify all parts of a water system and then establish schemes of control to manage each of those parts. If you are unsure then to be safe arrange for a Legionella Risk Assessment before you do anything with your system, it doesn't take long and you'll have some confidence you are doing the right thing. 

We already have a Legionella Risk Assessment so are we ok?

If water usage has changed then the Risk Assessment is likely to be invalid for the current situation. The good news is that your Legionella Risk Assessor will already have a good understanding of your building and should be able prescribe a temporary scheme of control to recover the situation.

We've been flushing our building water outlets at least once per week and water quality seems normal, do we need to do anymore before using it?

Suggest flushing hot and cold outlets one more time and if water quality seems ok then it's probably fine. It's a good idea to arrange for a Legionella Risk Assessment if you haven't got one and if you have one it would be worth making contact with your Assessor to explain the situation as they could point out something you hadn't thought of.

How do I safely flush through my water system?

You should assume any stagnant water flushed may contain Legionella bacteria, and you need to avoid exposing yourself or others to this flushed water. Seek an expert



If any flushing takes place then it should be done in a manner that avoids producing a water aerosol.  As an example you can control some aerosols by placing towels over outlets or discharging outside taps or shower heads into a refuse sack.

Dependant on the design of your water system there could be a number of flushing methods. 

Think about how water normally flows through your building. Where the hot and cold water supplies come from, are there cold water tanks, hot water vessels, hot water circulation systems, point of use water heaters and outside taps.

Once you know how hot and cold is distributed through your building and what any tanks serve, it can be a good idea to flush outlets nearest those sources drawing fresh hot and cold water for a few minutes. Then close those outlets and systematically moving through the building drawing fresh water as you go working towards the furthest points away from those hot and cold sources. It is probably better to work on one system at a time but this can get complicated. If you're not sure then seek expert advice (don't forget to operate appliances too).


Sources of supply

Cold water sources

  • Water Main - This could be directly from the public main and without any onsite cold water tanks, in which case you should start drawing water from outlets closest to the incoming supply or main internal stop valve.
  • Tanks - Any tank should be cleaned and disinfected before you attempt drawing water from it – you don't want to draw any additional stagnant water through your water systems. (Seek expert advice). Once the tank is clean, determine the flushing plan to draw water from outlets nearest that tank and working towards outlets furthest away.

Hot water sources

If the hot water vessel / system has been used less than normal for a week or more then it's likely to contain Legionella. The first step is to take expert advice on how to disinfect the vessel and system. Once disinfected hot water should then be drawn systematically through the system (nearest to furthest outlets), until fresh hot water is drawn through for at least a minute at each hot outlet.

How do I know that I've drawn fresh water through outlets?

It's generally accepted that water appears clear and normal and:

  • Cold systems - When the cold temperature drops to within a degree or two of the incoming supply to the premises or tank
  • Hot systems - when hot water outlets remain above 50o C for a minute or so. (55o C in healthcare premises)

We have a mains fed appliance what do we do (vending machine, drinks machine, water cooler or other)?

The water supply pipe serving the appliance is likely to contain unsafe water. You should disconnect the appliance and include the supply pipe in your flushing regime. Then arrange to contact the manufacturer for advice on recommissioning / servicing this appliance.

We have a cold water tank what should we do to ensure water is safe?

If you have a water tank then the safest thing is to arrange for this to be cleaned and disinfected. Nowadays there are a number of ways this can be done, but it usually involves draining down the system, manually cleaning the internal surfaces and then applying a method of disinfection. The method of disinfection may depend on the design, materials of the tank or the water system that it serves or convenience. As a minimum the tank should be drained (by turning off the incoming supply) then draining via an outlet connected to the lowest point on the tank before refilling. Any outlets attached to the tank should be flushed after tank drain down and refill.

Further information on cold water tanks can be found.

What about disinfecting hot and cold water services?

It will be the safest option for any water system and is likely to be required for larger systems especially where water is coming from a tank or there is a large hot water plant.

Who can disinfect my system for me?

A list of Disinfection Service Engineers; they will assess your system and work out the best options for you. Technical information can be obtained from BS8558 (2011) & BS8558 (2015).

I have a water softener what shall I do with that?

Most water softeners will require routine servicing and maintenance and dependant on the make and model the requirements vary. Please note down the manufacturers labels on your softener and look for any service stickers. Make contact with the service engineer or the local distributor for your softener and they will likely offer you a fairly swift service. For further information see here: Section 11 of Information for Installation of Ion Exchange Water Softeners for Systems Supplying Water for Domestic Purposes.