Arsenic, drinking-water and health risk substitution in arsenic mitigation: A discussion paper
A key policy lesson for public health protection that emerges from the arsenic crisis in Bangladesh is that in improving water supply services, consideration must be given of the degree of public health risk substitution that may result. In the case of Bangladesh, the provision of tubewells tapping the shallow aquifer substituted one public health risk (diarrhoeal disease) by another from arsenic. This risk substitution was not predicted at the time and the evidence of the potential for such a substitution was certainly not adequate for an evaluation of the probability and nature of potential substitutes.
In developing the arsenic emergency programme it is essential the potential for risk substitution is properly evaluated and that the selection of water supply options is undertaken within an overall risk management framework. Increasing scientific knowledge of the nature of different risks and how these may be controlled, makes such evaluation both practical and urgent in the arsenic emergency response.
This paper discusses some of the key issues that arise in relation to potential risk substitution from alternative water supply options, taking into account the varying nature of risks and the potential for their management. Within this framework, the efficacy and ease of medical treatment is considered as well as the management actions that can be taken to reduce exposures to hazards in drinking water. The paper draws on the developing paradigm of water safety plans, the approach that forms the basis of the revised 3rd edition of the WHO Guidelines for Drinking-Water Quality (GDWQ).
The key tool within the revised GDWQ is the development and implementation of Water Safety Plans (WSPs) related to health-based targets for water safety. The development of this approach has particular relevance to microbial hazards. WSPs are comprehensive management plans from catchment to consumer that when put in place will assure water safety and outline the necessary means of monitoring and verifying that such risks have been managed at a level determined as tolerable in the context of overall disease burden. Documents supporting this report contain examples of WSPs for small systems.