A Review of Different National
Approaches to the Regulation of THMs in Drinking Water
- The approaches to the regulation of trihalomethanes (THMs)
internationally have been reviewed.
- The new US approach to the regulation of THMs has been
reviewed in depth, including the formulation of plans and the
monitoring requirements for systems serving different sized
populations. The costs of implementation of the new regulations and the
benefits to human health estimated by the US Environmental Protection
Agency are summarised.
- The data on total THMs levels in the drinking water of all
the water companies in England and Wales from 2004-2007 have been
collated. These data were then analysed to compare the
stringency of the current total THM standard with that of the new
US approach if it were to be introduced in England and Wales.
These data were analysed to compare exceedances from the
present 100 μg/l absolute standard with a
locational running annual average of 80 μg/l used in
the new US regulation.
- Compliance with the present 100 μg/l standard for
TTHMs is very high; there was 99.92% compliance. Moving annual
average TTHM concentrations were calculated for
individual zones over the period 2004-7. Exceedances of a
moving average of 80 μg/l were in all cases less
than exceedances of the 100 μg/l standard, both in
terms of numbers of individual samples and on a zonal basis.
- Analysis of the results from samples collected from
geographically similar locations over the years 2004-2007,
although limited, suggested that a requirement to comply with
an locational running annual average of 80 μg/l would
be no more stringent that the present requirement of an
absolute standard of 100 μg/l.
- It was also concluded that distance of the sampling point
from the treatment works is not a reliable indicator of the
location of likely high TTHM concentrations.
- The implication for the England and Wales of a standard for
haloacetic acids (HAAs) such as that set in the USA was
assessed. The limited published data on HAAs levels in
UK drinking water suggest that a standard of 60 μg/l
would lead to a high number of exceedances. However, this
study was completed in 2003, and the initial findings of a
new study suggest that concentrations of HAA levels in UK
drinking water are now much lower than those originally
- The factors affecting the formation of HAAs in drinking
water and their removal in treatment process have been
- The potential costs to the water industry in England and
Wales of adopting the US approach to THM regulation were
assessed. The analysis of total THM data for England and Wales
concluded that the US approach to THMs was no more stringent than
the present regulations. Therefore, there were
no protective benefits to the UK of adopting the US
approach and no potential increases in cost, as there would be no
increase in exceedances.
- The cost implications for the water industry of setting a
standard for HAAs are unclear at present.
Copies of this report may be available as an Acrobat pdf download under the 'Post 2000 Reports' heading on the DWI website.