WaterSubject

Because of rising populations in developing countries, many surface water resources are becoming highly vulnerable to anthropogenic chemical and microbial pollution. Consequently, many low-income communities have become increasingly reliant on shallow groundwater resources defined in this research as the water bearing materials that are strongly influenced by physical and chemical processes on the ground surface. These shallow groundwater sources are often exploited using low-cost technology facilities such as wells or tubewells, where the water quality is monitored based on ‘end-product testing’ of selected microbiological and chemical parameters and controlled through the establishment of groundwater catchment protection zones.

Fundamental weaknesses in both the ‘end-product testing’ and groundwater catchment approach have been highlighted in the third edition of the World Health Organisation (WHO) Guidelines for Drinking Water Quality and the British Geological Survey (BGS) study of Associated Risks to Groundwater from On-Site Sanitation (ARGOSS). Limitations highlighted by WHO include analysis based on a restricted range of indicator organisms and overreliance on a nonrepresentative sample volume. Similar limitations in conventional approaches to groundwater catchment protection zones for developing countries have also been highlighted recently. Studies by the BGS on the ARGOSS suggest a high risk of short circuiting of the wellhead protection zone through localised pathways such as poorly sealed annuluses of boreholes or cracks in surface aprons (associated with construction faults and inadequate maintenance of wells).

To counteract these weaknesses, the WHO propose a fundamental shift away from end-product testing towards alternative risk-based approaches termed Water Safety Plans (WSPs), where risk is defined as a combination of the probability or frequency of a particular event occurring with the consequences of its occurrence. This is supported by the ARGOSS study, which concludes that effective groundwater risk assessment and management must include two main pathways of contamination:

In light of this debate, the objective of this paper is to develop improved methods for the assessment and management of microbiological water safety based on a ‘risk’ paradigm. The conceptual basis of risk is defined in this context by the source pathway receptor model, where the source is defined as the hazard event/environment (e.g. septic tank), the pathway as the vulnerability of the media (e.g. soil type) and the receptor as the receiving water infrastructure (e.g. hand-dug well).

This study was undertaken in Niassa province in northern Mozambique through joint research between the UK Water, Engineering and Development Centre (WEDC), the Mozambique Estação Agraria de Lichinga (Agricultural Research Centre) and the UK charity WaterAid. The precise study area selected was the town of Lichinga (population 110 000), the capital of Niassa province, located at 13°18′S, 35°15′E. Three sample communities (Nomba, Lulimile and Ceramica) were selected from within Lichinga based on practical/logistical criteria to achieve a statistically valid sample size (i.e. number of statistically valid water points). To calculate n water points for a population of size N within these communities, the Student’s t-test was selected. For a statistically valid sample of the total 362 water points in Lichinga, 20 water points would be required (plus five control ‘traditional wells’ at 25% of the sample size). Categorical (nonchanging) and parametric (continuous) data were collected at each of the 25 well sites over a 12-month period from November 2003 to October 2004. Historical data were made available to the researcher from August 2002 to October 2003. The methods selected for each variable are outlined.

The objective of this paper was to develop improved methods for the assessment and management of microbiological water safety based on a ‘risk’ paradigm. To achieve this objective, this paper concludes that the following points are critical for the effective assessment and management of groundwater microbiological risk.