Water
Quality – filtration, treatment and testing
Introduction
POU water dispensers use the water at point of entry into
the building. Depending on the quality
of the water, a choice has to be made on further treatment required at the
point of use. The quality of mains water
in the UK is good and the treatment processes effective, however, there are 25
water companies in England and Wales alone, each with its own treatment
regimes. It is essential that the POU
distributor is aware of the water quality when installing new dispensers. In fact, this should be part of the risk
assessment when deciding on appropriate filters and dispenser types.
Information
from Water Companies
The water companies are required to provide you with
information for purposes of your risk assessment, as indicated by the
Environmental Information Regulations 2004.
Information can include a description of their treatment process, data
on historical cryptosporidium breakthroughs and whether special treatment has
been used, such as additional filtration and use of UV. Data on additives used to reduce lead
migrating from old pipework and whether chloramines are used in the
disinfection process should be available on request. All this information should enable you to
make a make a more informed decision about filter choice.
Typical
Water Treatment
There is no typical water treatment because each
company’s treatment process will have been worked out based on risk assessments
of the source waters. Generally,
coagulation and filtration are the first stages using mixed media filters
followed by a primary chlorination. This
chlorination stage will provide initial germ-kill and remove organic material
by forming organo-chlorine compounds which are then removed by granular
activated carbon beds. Immediately
afterwards the main dose of chlorine is added and allowed several hours contact
time.
Special
Treatments
Special treatments are put in place according to source
water characteristics, for example, if animal waste contamination occurs
frequently, special filtration and UV treatment would be employed to reduce
risks of cryptosporidium breakthroughs.
If the distribution network is very long, chloramine treatment may be
used to enable a more lasting disinfection during transit. This is done by injecting ammonia in to the
chlorinated water which forms the chloramine in situ. Polyphosphate is
added to the water supplies if the pH is low, to avoid lead being dissolved
from the surfaces of old pipework.
Water
Testing
Water companies provide a source of information to help
you in making informed decisions about filters and dispenser
specifications. However, if you need an
immediate answer, test strips are available which will indicate free chlorine,
total chlorine (the difference will indicate whether chloramine is present),
water hardness and pH. However, you need
to contact the water company to assess the risk of cryptosporidium contamination
and for lead content.
