Report No FR0481

G O'Neill, N Mole, H Horth and M Fielding

Nov 1994



A full understanding of the current, and likely future, disinfection by-products of concern and their implications.


To review the occurrence and significance of disinfection by-products (DBPs) formed during water treatment and to identify any important implications for water suppliers in relation to current regulations and likely future developments.


DBPs are of concern to water suppliers mainly because of their potential health effects. Existing regulations have led to changes in treatment practice and monitoring. Additional standards are beginning to appear that reflect new information on formation and toxicity of DBPs, These, and future developments in this field need to be reviewed and any important implications for water suppliers identified.


Disinfection by-products continue to pose problems to water suppliers with implications of increased treatment and monitoring costs. However, the implications depend on the stringency of future standards.

New health-based standards for disinfection by-products have been issued by the WHO in 1993. The UK government has usually placed great store by WHO standards but it remains to be seen whether these will be incorporated in an EC Directive, and hence in UK Regulations. If these standards were included then, on the basis of available data, only bromate would pose serious problems for water suppliers, mainly in relation to the use of ozone but possibly also in relation to the use of hypochlorite solutions.

However, the EC Drinking Water Directive does not cover disinfection by-products in a sensible manner and the existing relevant parameter is highly likely to undergo revision (a revision of the Drinking Water Directive being underway). The implications of a revised and probably more detailed parameter, i.e. covering individual by-products, is not known since the details are not available. However, this report outlines some possibilities (Section 3.3).

Regardless of impending standards, there are a few important gaps in knowledge (of toxicology and chemistry) which need to be filled in order to evaluate the future impact of disinfection by-products. These are given in Section 4.2.


Development of standards for DBPs in Europe and the USA needs to be closely monitored.

New data on the formation and toxicity of DBPs needs to be routinely evaluated in relation to potential implications for UK water suppliers.

Any direct or indirect input from UK water suppliers (e.g. via EUREAU) into the development of standards (WHO, EC Directive revisions) can only be worthwhile.

Some areas of study are necessary; information on the occurrence of specific DBPs and more fundamental investigation of the nature of DBPs (e.g. on the toxicology of the by-products of polyelectrolytes). These are detailed in the report (Section 4.2).


The report reviews the occurrence and toxicity of DBPs from the major disinfectants (with emphasis on recent developments) and considers implications for water suppliers. The detailed information on standards, occurrence and toxicity is given in an appendix. This supports a summary of the current situation and possible future developments.

Copies of the Report are available from FWR, price 25.00 less 20% to FWR Members