Report No DWI0209

DISINFECTION BY-PRODUCTS

Proceedings of a Drinking Water Inspectorate Seminar Held at WRc Medmenham 2 and 3 February 1993

DWI0209

Feb 1993

SUMMARY OF DISCUSSION - DAY 1

The discussion on the first day largely centred around public perception on drinking water quality and the issues involved in this subject. A summary is provided below under four main subject areas:

Public education

The issue of how the public become involved in the debate on drinking water quality was discussed in detail. It was noted that the public are generally not aware of the background to most of the issues. but that the subject is of great interest. simply because all of us are consumers'. Given that the public are involved. the onus was felt to be on the water supplier to provide more (and better) information on the range of issues covered by the general phrase "drinking water quality". Too often the only sources of information have been pressure groups and a press inevitably looking for 'problems' . It was pointed out that customer queries and complaints that are met on an individual basis. often result in a satisfied customer who, for example. would then understand the need for disinfection. In the US, the law requires public notification of any changes in water treatment and standards. The question clearly remains. however. whether the public take any notice or indeed understand the reasons for the changes. Political action groups are powerful in the US and put pressure on Congress. The action groups do not necessarily look in depth at the issues or consider what the public think. but assume that the public have an intrinsic right to 'pure' drinking water. The concept that there is no such thing as 'pure' water and that the aim is to provide safe water needs to be emphasised. No specific conclusions were reached during the discussion. but it was generally agreed that there is an urgent need to educate consumers and that water suppliers have a prime role in this context.

Bottled water

The reasons for the recent popularity of bottled water were discussed. People often assume that bottled water is safer than tap water, with many in some countries (ca 30%) only drinking bottled water. There is some doubt whether a persons preference for bottled water arises from health concerns or simply that they like the taste. If the latter is the case, then the water suppliers have to improve the taste of their product in order to compete. However. it was also recognised that tap water and bottled water were different products and should not really be in competition. It was suggested that the use of ozone might improve taste and odour of drinking water. making it more acceptable to the consumer. Chlorinous taste problems remain one of the major areas of public complaints. although it was recognised that some people feel that a chlorine taste provides reassurance that the water is safe to drink. Risk assessments have not been carried out on bottled water- possible concerns include leaching from the plastic bottles, high mineral concentrations and microbial content. It was pointed out that further legislation for bottled water was being considered.

Risk assessment

The concept of risk assessment (in this context the relative risks from the presence of disinfection by-products (DBPs) in water relative to microbiological safety) needs to be explained to the public -however. it is a complicated area. Risk assessments should also be carried out for other water uses (e.g. showers. cooking). The perceived risk of cancer is very much greater than that of water-borne microbial disease. This is partly because people probably have faith in medical science being able to fight waterborne microbial diseases, but also because there is a much greater fear factor with cancer: everyone probably knows of someone who has died from cancer. but typhoid and cholera etc. have been virtually eradicated in the West. It is important that the public are made aware of the very real risks posed by ineffective disinfection. and how they compare to the theoretical health risks from DBPs in drinking water. The high impact of cancer on public perception must not be underestimated (contrasted with e.g. the impact of lead). The media play a critical role in influencing the public and it is possibly through the media that the balance will have to be redressed. It was suggested that there were clearly much greater risks in life than drinking tap water. However. people have to drink water and therefore feel that it should not pose any risks, whereas other risks can be minimised through choice.

Costs

Any costs involved in imposing tighter standards for DBPs in drinking water will ultimately be met by the consumer. Will the consumer choose to pay for higher standards or prefer cheaper water with less stringent standards? Again. any useful consumer input has to be obtained from informed sources and this reinforces the need for education. The public should be told of the cost of improving standards. but in a way that they will understand. In order to do this. the water suppliers need to produce costs related to tangible. and recognisable. benefits to the consumer. A reduction in overall risk may not mean much to the average consumer, who is probably far more interested in improvements in palatability. The main concern of consumers will be the taste. odour and appearance of their drinking water. These features could well be relatively unaffected by the extensive investment in methods for reducing levels of DBPs.

In the US, statutes govern any change to water treatment practice. The main goal is that an acceptable risk should be 'zero'. and hence regulations arc introduced that arc aimed at achieving this. The public arc not involved directly in this decision making process. although they are consulted.

SUMMARY OF DISCUSSION - DAY 2

The bulk of the discussion on the second day of the seminar was related to the US EPA approach to disinfection by-products (DBPs) and risk assessment. A summary of the main points of this discussion is given below. Topics arising from other presentations are also summarised.

EPA risk assessment policy

The EPA is currently considering regulation of a wide range of DBPs in addition to those already regulated. The need to balance mandatory requirements for disinfection. via compliance with the surface water treatment rule (SWTR) and the coliform rule, with future legislation on DBPs is critical in setting standards. The EPA is proposing to regulate 83 chemicals initially, with a further 25 additional compounds every 3 years. The US Safe Drinking Water Act specifies that a best available technology (BAT) for each standard is established that is economically feasible for large water systems. The BAT will have to include disinfection options and will be based on large treatment works with the possibility of application to smaller works. The BAT does not include the use of new technologies, and therefore there seems to be no pressure or incentive for utilities to develop new processes. Why the EPA needed to provide details of the BAT was queried - would it not be simpler to specify the limit and leave it to the individual utilities to employ processes to meet the limit? In reply, it was pointed out that the statute requires the EPA to specify the that in order to give utilities a chance of meeting the limits. The possibility was raised of providing a number of different options rather than a single BAT, mainly to avoid the possibility of a particular BAT failing to achieve the necessary standards in all cases (because of differences in water types etc) . It was stated that other treatment options can be used as long as the end result is at least as effective as the BAT specified.

The approach adopted by the EPA to risk assessment was raised. It was noted that in 1985, an estimated 1000 deaths in the US were caused by water-borne diseases. Other data suggest that up to 25% of the population can suffer illness due to microbial contamination of the water, but it is seldom reported or diagnosed as such. In 1985, 80% of breaches of maximum contaminant levels (MCLs) related to microbiological limits, and of these over 90% occurred in small systems. Data were available for Giardia and therefore this was included in the surface water treatment rule (SWTR). One of the major goals of the SWTR is to achieve a risk of Giardia infection of less than I case in 10000 per year. Since Giardia is hard to inactivate, it is thought that if this can be achieved then levels of other microbes will be even lower. It was pointed out,however, that Giardia is not a problem in groundwater, so other measurements are required to show satisfactory inactivation (e.g. for viruses).

An example of the type of model used to evaluate the relative risks of microbial activity versus DBPs was outlined. By lowering the MCL for trihalomethanes (THMs), a lower cancer risk should be attained. This decrease in risk, however, is small. If the reduction in THM levels is achieved through the use of a lower disinfection dose, then the microbiological infection risk increases significantly. Models estimate that 200 extra deaths from water-borne microbial diseases could arise for a reduction of 15 cancer deaths. The proposed rule has to be devised so that there is no increase in the risk of microbial infection, and ideally that there is a net decrease. It was suggested that there were some weaknesses in the microbial model due to lack of quantitative data. It was emphasised that DBPs with known risks must be controlled, as must those with unknown risks. The possibility was discussed of monitoring certain compounds as representatives of certain groups of DBPs (e.g. bromodichloromethane for THMs) to avoid extensive monitoring. The difficulty of trying to improve disinfection while minimising DBP formation was again emphasised.

The EPA has adopted an approach to developing the DBP rule that brings together representatives of the affected groups to negotiate an acceptable approach to the rule (the negotiated regulations approach). In this way state and federal regulators, utilities, public interest groups and health organisations are all involved in decision making, although it is not known how successful this approach will be.

Other areas of discussion

The possibility of minimising the need for disinfection through better control of source waters was raised. One option would be better protection of catchments. It was felt that this was one way forward. but in practice would be extremely difficult to achieve. Another possible solution would be to increase impoundment. Again. this would be desirable. but the costs would be high since long storage times would be required to achieve significant degradation of contaminants/bacteria.

It was emphasised that it is important to strike a balance between producing 'sterile' water (which is not healthy for consumers. since they need to build up some immunity) and 'safe' water. Another issue raised was whether it was possible to reduce the 'age' of water, i.e. the time spent in the pipe. Computer models help, enabling better management of water in the distribution system. It was suggested that the pipe has to be considered as a 'chemical reactor' and its management should be addressed accordingly

The use of UV irradiation as a disinfectant could be one option for minimising by-product formation. It was thought likely, however. that the public may be suspicious of this technique. although it is already used extensively in small water supplies. In addition, there is little information on possible by-product formation from UV disinfection.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.