Maintaining water quality in buildings with low or no occupancy

Mike Rose, Director at RPS has put together the following guidance to outline the steps to be taken to help minimise the risk of legionella growth and the general deterioration of water quality, within engineered water systems.

Mike Rose, Divisional Director - Health & Safety
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01 Apr 2020

With many offices and buildings currently experiencing low or no occupancy levels, there are a number of steps that owners should be taking to minimise potential risks when buildings become reoccupied. The immediate implementation of these steps provides assurance that the water quality remains of a good standard and, in most cases, without the need for a disruptive chlorination of the water systems.  

Where possible, and safe to do so, water systems in buildings should be kept operational and normal usage should be simulated. At present we wouldn’t advocate ‘mothballing’ buildings, which involves charging systems with chlorine and closing down access to the building. This should be seen as a last resort. Furthermore, at this time we also advise against draining water systems. This can cause leaks, biofilm growth and damage to pipes etc.

What to do next

Our guidance relates to water systems typically encountered. It doesn’t cover all scenarios and individual water systems which may have their own unique characteristics that need to be considered.

Mains fed building, no cold-water tanks / no large water heaters

  • Turn off small water heaters if not required. Flush through until mains cold water temperatures are attained at supplied outlets.
  • Flush sentinel outlets for 5 to 10 minutes on a twice weekly basis. Where possible, flush a number of other outlets on each floor for 2 minutes.
  • Flushing WC cisterns is a good way to get water movement in a building. Each WC (where possible) should be flushed weekly.
  • Remove shower heads and spray outlets (where not required)

Mains fed building, no cold water tanks with large water heaters

  • Turn off water heaters if not required.  Flush through until mains cold water temperatures are attained at supplied outlets.
  • If water heaters are required ensure hot water is stored at 60°C at all times.
  • Flush sentinel outlets for 5 to 10 minutes on a twice weekly basis. Where possible, flush a number of other outlets on each floor for 2 minutes.
  • Flush all WC cisterns on a weekly basis where possible
  • Remove shower heads and spray outlets (where not required)

Building with cold-water tanks and no large water heaters

  • Reduce the capacity of cold-water tanks to as low as possible or as low as required
  • Turn off small water heaters if not required. Flush through until mains cold water temperatures are attained at supplied outlets.
  • Flush sentinel outlets for 5 to 10 minutes on a twice weekly basis. Where possible, flush a number of other outlets on each floor for 2 minutes.
  • Flush all WC cisterns on a weekly basis where possible
  • Remove shower heads and spray outlets (where not required)

Building with cold water tanks and large water heaters

  • Reduce the capacity of cold-water tanks to as low as possible or as low as required
  • Turn off water heaters if not required. Flush through until mains cold water temperatures are attained at supplied outlets.
  • If water heaters are required ensure hot water is stored at 60°C at all times.
  • Flush sentinel outlets for 5 to 10 minutes on a twice weekly basis. Where possible, flush a number of other outlets on each floor for 2 minutes
  • Flush all WC cisterns on a weekly basis where possible
  • Remove shower heads and spray outlets (where not required)

Additional steps for all systems

  • Legionella sampling from sentinel points to confirm legionella control has been kept
  • Empty tanks and refilling tanks could be done instead of full system chlorination’s
  • Thermal pasteurisations of hot water systems
  • Review the situation/regime in one month)
  • Identify in advance those buildings that are more likely to require clean and chlorination’s once the situation returns to normal due to complexity of systems etc.

Cooling Towers

  • Isolate the fans where reduced cooling requirements permit
  • Circulate the condenser water system on a daily basis (at least 5 days a week e.g. Monday to Friday) for 2 hours. This should be completed so all areas of the system come into contact with biocide for at least one hour. Therefore, the system should be circulated for around 2 hours (depends upon system)
  • Ensure stocks of water treatment chemicals are at adequate levels, including salt for water softeners.
  • Continue the current monitoring regime, however where necessary some tasks can be reduced to weekly rather than daily e.g. biocide testing, softener tests etc.
  • Review the situation in one month – undertake legionella sampling to confirm control.

Site specific advice

Our team are on hand to advise on issues relating to your individual buildings or specific water systems. Get in touch to find out how we can support you with your site specific needs.

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