Chlorine Dioxide Dosing

What is the background information?

The managing agent of a prestigious residential block in central London were concerned that persistent high level counts (3 – 4000 cfu / litre (See Fig 1) of legionella was being detected in its hot water system. Managed Water Services were commissioned to undertake a risk assessment on the premises’ water systems, current regime and management systems and identified that immediate action was required to minimise the risks associated with the system. The use of the WaterMaster chlorine dioxide generator was discussed and with help from the M&E contractor and consultants concerned with the maintenance of the building, it was agreed that this would be the best solution.

(Fig 1) Example of positive Legionella results showing 3400cfu/litre (pre installation of the MWS WaterMaster Chlorine Dioxide dosing unit).

More about the premises and help that was offered from MWS

The residential block is located close to one of the most expensive and exclusive parts of London. The building is approximately 70 years old and various refurbishments have taken place on the water systems over the years. The managing agent were keen to protect themselves from any legal action due to unmaintained water systems, but were also keen to protect the tenants, ensuring they have the best protection available. Each block is managed by a porter/handyman and a maintenance contractor is also present. Due to the nature of the tenants some flats may be vacant for long periods.

Managed Water Services have experience in undertaking installation and service of chlorine dioxide generators and were able to offer the managing agent and the resident’s management representatives case studies and references for their peace of mind. All parties were also shown examples of other WaterMaster installations that Managed Water Services had carried out so they specific knowledge of the type of plant being installed. The WaterMaster was installed and commissioned within ten days of receipt of order.


The managing agents and residents management representatives, like any other residential block with a communal water system, have a duty to protect the residents, staff and visitors to the building. The WaterMaster was effective at cleaning up the system and within 8 weeks of installation we were able to let the managing agent know that the most recent sample had tested negative for legionella. We continue to work with the site management ensuring the risks from the site’s water systems are minimised. This is achieved through continual dosing of chlorine dioxide, web based monitoring, visual inspection, the implementation of a site water management log book and regular review meetings. The managing agent is very satisfied with the service received from Managed Water Services and we are helping them with several other sites in their portfolio.

(Fig 2) Example of sample results showing no Legionella bacteria present in the same water sample post installation of the MWS WaterMaster Chlorine Dioxide Dosing unit.