Water quality

Craig Salter made this Freedom of Information request to Welsh Water
You only have a right in law to access information about the environment from this authority
This request has been closed to new correspondence. Contact us if you think it should be reopened.

The request was successful.

Dear Welsh Water,

Could you please provide me information of how you treat our water for drinking consumption.

A full breakdown on what chemicals and additives you use to make our water "safe" to drink would be appreciated.

Yours faithfully,

Craig Salter

Environmental Information Requests, Welsh Water

Our Reference: EIR/836/2021



Dear Mr Salter


Request for information

We write further to your request for information dated 12^th July 2021,
which we have been considering under
the Environmental Information Regulations 2004.


We refer to your question for information on how we treat our water for
drinking consumption, we have an informative video and supporting
documents on water treatment on our website at the following link:



We can also provide you with Water Quality Information for your area by
entering your postcode at the following link:



Chemical dosing is a necessary part of the treatment process to ensure
that safe and wholesome drinking water is supplied to our customers.  As
such, all chemicals used are compliant with the Drinking Water
Inspectorate and Regulation 31, which is a list of safe chemicals and
materials for use in the treatment of drinking water for human consumption
and is free to view online.  As the treatment process is continuous,
chemicals are dosed constantly through automated systems, using monitoring
instruments throughout the process to ensure that concentrations remain
within suitable limits.


The process is automated, and the monitoring/control instruments ensure
optimal water quality without any chemical overdosing, which all
contributes to keeping the process as efficient as possible.  Personal
Protective Equipment (PPE) is worn during the delivery of bulk chemicals
or when dealing with a blockage/burst, in line with our specific COSHH
activity assessments that are in place for every chemical at every site.


The treatment process doses a coagulant (ferric sulphate, aluminium
sulphate or aluminium chloride) to the raw water to aid with coagulation. 
There may also be a pH correction stage, which is done using either
calcium hydroxide or sodium hydroxide, to achieve the correct pH for
coagulation to occur.  The coagulation process precipitates the colour
from the raw water into a solid form, which may also be assisted through
the addition of polyelectrolyte, and then physically filtered and


This is done through different stages of filtration.  In-between the
stages of filtration, chlorine is dosed as an oxidising agent to assist in
the removal of manganese from the water through the next filtration stage.


After filtration, chlorine is dosed to ensure full disinfection of any
bacteria that may be present in the water before the water is analysed and
permitted to go into supply.  Samples are taken regularly for
microbiological testing at our laboratory to ensure that this process
remains effective.  Welsh Water do not dose fluoride at any of the
treatment works.


The final chemical addition before the water leaves the treatment works
can be pH correction, as above, and / or orthophosphoric acid, which is
dosed to form a protective phosphate layer in any lead pipes in customers
properties and prevent the leaching out of dissolved lead.


The dosing of chemicals will vary depending on the raw water conditions.
 Every year we take thousands of samples to check the quality of the water
we’re supplying to our customers. We have to submit the results of these
samples to our regulator, the Drinking Water Inspectorate (DWI), and if
any fall below the standard set by the DWI we investigate to both our and
their full satisfaction. These results are also available to our customers
in our annual water quality zone compliance summaries.  We hope that this
response is clear.


Should you have any questions, please contact us by email at
[3][email address]


If you are dissatisfied with the handling of your request, you have the
right to ask for an internal review. Internal review requests should be
submitted within 40 working days of the date of receipt of this response
and should be addressed to Company Secretary, Linea, Fortran Road, St
Mellons, Cardiff CF3 0LT

If you are not content with the outcome of the internal review, you have
the right to apply directly to the Information Commissioner for a


Yours sincerely,


Dŵr Cymru Welsh Water


_______________________________________________________ Dwr Cymru Welsh
Water is firmly committed to water conservation and promoting water
efficiency. Please log on to our website www.dwrcymru.com/waterefficiency
to find out how you can become water wise. Mae Dwr Cymru Welsh Water wedi
ymrwymo i warchod adnoddau dwr a hyrwyddo defnydd dwr effeithiol. Mae
cyngor i' ch helpu i ddefnyddio dwr yn ddoeth yn

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