Disinfections

The cleanliness of the system must be maintained as legionella bacteria are more likely to grow in a system fouled with deposits.

Any new water system will require at least flushing and disinfection before being brought into use and the building commissioning process should take into account the size and complexity of the water system.

The risk from exposure to legionella should be controlled by keeping the water system and water in it clean and free from nutrients, including those arising from contamination and corrosion; and maintaining its cleanliness. Hardness scale may also trap nutrients, encouraging biofilm formation and so form a barrier to disinfectants.

Where necessary, hot and cold water services should be cleaned, flushed and disinfected in the following situations, as specified in BS 8558:2011:

  • On completion of a new water installation or refurbishment of a hot and cold water system;
  • On installation of new components, especially those which have been pressure tested using water by the manufacturer (see the manufacturer’s instructions);
  • Where the hot and cold water is not used for a prolonged period and has not been flushed as recommended or the control measures have not been effective for a prolonged period. For example, this could be as little as two or three weeks, but will depend on the ambient temperature, condition of the water system, potential for exposure to aerosols and the susceptibility of users considered in a specific risk assessment;
  • On routine inspection of the water storage tanks, where there is evidence of significant contamination or stagnation;
  • If the system or part of it has been substantially altered or entered for maintenance purposes that may introduce contamination;
  • Following water sampling results that indicate evidence of microbial contamination of the water system
  • During, or following an outbreak or suspected outbreak of legionellosis linked to the system;
  • Or where indicated by the risk assessment.

Thames Water Disinfections

If your supply is of 50mm internal diameter and above:

Under the Water Supply (water fittings) Regulations 1999 (SI 1999, 1148), you will be required to disinfect your underground pipe work prior to connection.

The disinfection must be carried out to ‘BS 8558:2011’. This is to ensure there is no detriment to public health.

For further details and clarification, please refer to section G13.1 of the Guidance Notes to S1 1999, 1148 and clause 3.1.10 of BS 8558:2011.

New supplies should be swabbed, flushed, filled with chlorinated water not less than 50mg/l and allowed to stand for 1 hour, following which the chlorinated water should be flushed out, the pipe refilled, and a sample taken.

The pipework must be disinfected with a ‘hypochlorite’ solution’.

The following must be submitted to our office prior to the connection being made:

  • A disinfection certificate
  • A method statement of the disinfection process carried out
  • The sample results

The ‘certificate’ must indicate the name of the company performing the disinfection, date of disinfection, confirmation that the pipe has been swabbed and flushed prior to disinfection, a ‘hypochlorite’ solution has been used, the chlorine level of the source water, the chlorine level after dosing, the contact time, the chlorine level after contact, and the chlorine level after flushing. It must also detail the onsite test for appearance, odour and taste.

The certificate must clearly state that the disinfection has been carried out in accordance with BS 8558:2011.

The ‘method statement’ must indicate the details of the disinfection carried out, the diameter and length of pipe disinfected, the source of the water used, the sample location point, and a diagram.

The ‘sample results’ must include E-coli, total coliforms, turbidity, and plate counts taken at both 22°C and 37°C. The post flush chlorine level must also be confirmed by laboratory analysis.

The sample results must be from a ‘UKAS’ accredited laboratory.

It is also the customer’s responsibility to ensure that the designated disinfection company is aware of Thames Water’s requirements.

If this procedure is not met Thames Water have a right to refuse the final connection, and the pipework must be re-disinfected to meet their requirements. They will not begin the connection process until they have received these documents complete with all information.

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