Water and ventilation system safety in reoccupied buildings

Last updated: 13 September 2021

covid water safety

Ensuring water and heating system safety in reoccupied buildings under COVID-19 restrictions.

As COVID-19 Alert levels drop, it is important to ensure that the water systems in your building are safe for when people return.

When water is not drawn through a building's water system over an extended period, the water becomes stagnant making it potentially harmful to people. Water stagnation is usually prevented through regular water use, which brings in a consistent supply of fresh water from the public mains.

Indicators of stagnation include a bad or "off" taste, unpleasant odour or slight discoloration which can indicate bacteriological growth and pipe corrosion. Stagnation can support the accelerated growth of many microorganisms and pathogens, such as Legionella, which can cause harm to building occupants. It is also possible that water left sitting for long periods of time within a building’s water system could contain excessive amounts of heavy metals.

Regardless of whether the signs of stagnation are present, it is recommended that you ensure your building's water supply is thoroughly flushed before people return to work following the lockdown.

Flush your water system before your business or building reopens

Flush water through all points of use within the building before reopening such as showers, sinks, toilets. The process for doing this will vary depending on the building, and may need to occur in sections (e.g. floors or individual rooms) due to building size and water pressure. The main goal of building flushing is to replace all water inside the building’s pipes with fresh water.

Example procedure for flushing a building water supply system:

  1. Remove tap aerators, point-of-use filters and shower hoses where possible, which will increase the flow of water and limit the amount of sediment trapped during flushing.
  2. Organise flushing to maximize the flow of water, by either opening all cold water outlets simultaneously to flush the service line and internal pipework, or flushing all outlets individually, starting near where the water enters the building and moving systematically through the building to the most distant outlet.
    Note: Flush the cold water pipework first, and then the hot water. 
  3. Run enough water through all outlets to replace all water inside building piping with fresh water. The required duration will vary based on pipework volume and outlet flow rate.
  4. Replace all tap aerators and point-of-use filters and shower hoses.
  5. If you see excessive disruption of pipe scale or if there are concerns about biofilm development, additional precautions maybe needed including continued use of bottled water, installation of a point-of-use water filter, or engaging a contractor to thoroughly clean the plumbing system.

Floor drains

If the building has floor drains, it is possible the water seal within the trap of each drain will have evaporated without use, potentially letting sewer gasses enter the building. Pour water into each drain to make sure that the trap water seals are fully restored.

Building Services (HVAC/fire/electrical/gas systems etc)

Each building is different. Depending on the level that a building was shut down prior to lockdown, additional work may be necessary to ensure buildings are safe to use before people return. It is recommended that building managers contact their maintenance providers to ensure buildings are safely recommissioned before reoccupancy as needed.

Ensure good ventilation

Buildings with ventilation systems are designed to provide fresh outdoor air to the building and to extract out stale or contaminated air. Well maintained ventilation systems are essential to providing safe working environments.

It is recognised that most building ventilation designs were never intended or designed to cope with a COVID transmission scenario and this guidance does not expect existing ventilation systems to be retrofitted.

The following guidance is intended to assist building owners to optimise the operation of existing ventilation systems and is based on current international best practice.

Building ventilation and air conditioning systems should be kept well maintained. In practice, this means any ventilation and air conditioning systems should be operating as designed and be regularly cleaned. Fans and ducts need to be kept clean and clear, filters should be cleaned or replaced as required and flow rates need to be balanced. Owners should also consider seeking specialist engineering advice to determine the building’s compliance with existing professional recommendations, and to identify opportunities to improve indoor air quality.

Ideally, air should be not re-circulated within a space and exhaust air should be vented directly outside wherever possible. Where air recirculation cannot be eliminated, it should be reduced and the use of outdoor air increased as much as possible.

The mechanical outdoor ventilation rate should be increased above the minimum rates wherever possible, but this must be balanced against the need to ensure the thermal comfort of occupants.

Possible actions which may be considered include (but are not limited to):

  • Increasing ventilation rates for office spaces above 10 L/s per person. If ventilation rates cannot be increased, the maximum room occupancy should be decreased.
  • Centralised air handling units could, whenever possible, be switched to 100% outdoor air mode.
  • Demand-control ventilation functions that reduce air supply based on temperature or occupancy should be disabled.

If the building does not have mechanical ventilation for the provision of outdoor air, windows should be opened regularly to circulate fresh air.

Other considerations:

  • Do not switch off ventilation at nights and weekends, but keep systems running at low speed.
  • Avoid opening windows in toilets to ensure the right direction of ventilation.
  • Replace filters of any central outdoor air and extract air, local fan coil and air conditioning units as usual, according to maintenance schedule.
  • If fan coil units or local air conditioning units are present, replace their filters according to maintenance schedule.
  • Perform regular filter replacement and maintenance works addressing common protective measures including respiratory protection.

This information is published by the Ministry of Business, Innovation and Employment’s Chief Executive. It is a general guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case. Expert advice may be required in specific circumstances. Where this information relates to assisting people: