Recovering drinking water supplies in buildings and networks after prolonged inactivity

The restrictions placed on business and people by UK governments as a measure to restrict the spread of SARS-CoV-2 in mid-March 2020 left many premises either closed or with reduced staff. The pace of change meant that many drinking water systems may have been left stagnant over this period.

This note provides guidance to building owners, landlords and managers and to those who operate “Refill” schemes as to the steps necessary once access to buildings is permitted as to how to restore their drinking water systems[1]. For guidance on managing risks associated with Legionella please contact the appropriate authorities.

A more detailed assessment of the regulatory and legal duties has been provided for use in England and Wales by DWI (Advice Letter 02/2020).


As a result of closure or part closure of buildings drinking water systems may have been subject to stagnation due to low turnover of mains water or water in storage. This could have resulted in warming of water in internal plumbing systems, microbiological regrowth or increased uptake of plumbing metals. Unless steps are taken before the building is reoccupied there is a risk of adverse drinking water quality and potential risks to health.

Mitigation steps:

As the country reestablishes itself after the restrictions put in place to manage the pandemic the local water company will be continuing to maintain its own networks and systems to assure the quality of water entering a building. It is critical that building owners, managers and landlords also take action to manage the risk of water systems that have not been used, to ensure that as staff return, water systems are safe. In the first instance there are some simple steps that can be taken to recommission your drinking water system:

  • To ensure that the water in the plumbing systems is fresh, run all taps individually, starting with the tap nearest to where the water enters the building and moving systematically to the most distant outlet. It should be sufficient to run until the water is clear and feels cool to the touch. Where water is supplied from storage, storage cisterns should be emptied and filled with water direct from the incoming supply, before the taps are flushed;

  • Flushing should be carried out in a manner which minimises aerosol generation, e.g. removing shower heads prior to flushing, to reduce the risks of Legionella transmission. Safety considerations should be made for those flushing including appropriate PPE;

  • Ensure that all appliances are also thoroughly flushed through before use, using manufacturer’s instruction manual;

  • If the property has any internal filters or water softeners, these should be checked to ensure they are working correctly as outlined in the manufacturer’s instruction manual;

  • Ensure that if plumbers are required to make any changes or repairs to the plumbing system that approved plumbers under the WaterSafe scheme are used;

  • Confirmatory testing is widely available for water systems.

Larger buildings, those with tanks, showers, calorifiers and more complex pipework the expectation is likely to be for more extensive flushing followed by cleaning and disinfection. If you have a complex plumbing system you should ensure you have a competent person to oversee this work. Recommissioning your water supply should be in-line with your water safety management plan, including pressure testing all systems.

If you still have concerns after taking these simple steps, please contact your water retailer or look on the local water company website for more information.

Water retailers can access specialist advice on how to support their clients and the specific issues affecting them from their designated wholesale supplier contact point.

Dr Jim Marshall

Senior Policy Advisor and Covid Operational Lead

Water UK

May 2020

Further information

DWI Advice Letter 02/2020 – “Maintaining drinking water quality when reinstating water supplies after temporary closure due to the CoViD-19 outbreak”

Water UK / WRAS “Looking after water in your home” -

Key advice and guidance can be found from the following websites:

Regulators and government bodies:




CMA Scotland -

HSE - (Legionella HSG274 –


WaterSafe approved plumbers –



BS 8580-1:2019 Water quality. Risk assessments for Legionella control. Code of practice

BS8680 - Water quality – Water safety plans – Code of practice Not yet published

BS EN 806-2:2005 Specifications for installations inside buildings conveying water for human consumption. Design

PD 855468:2015 Guide to the flushing and disinfection of services supplying water for domestic use within buildings and their curtilages


Legionella Control Association




Awareness / interest


[1] We also recommend that building owners are mindful of the risks to all non-drinking water systems as well such as heating systems, leisure systems and water used in production in line with their existing water management plans and from the relevant associations. Guidance on these systems should be sought from the relevant expert bodies, some of which are listed at the end of this document. 


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