Safe Drinking Water-A Local Example of a Global Challenge

Article excerpt

INTRODUCTION

Over the past 20 years water demands have steadily increased and the controversies and conflicts over drinking water are now a foremost concern of the public. The rapid shift by urban consumers towards the consumption of bottled water rather than drinking tap water suggests that the public has lost confidence in the safety of their water supplies. The Walkerton, Ontario incident, where 7 people died and over 2300 were hospitalized because E-coli found its way into the community drinking water supply system, made the public aware that even in Canada it is possible to contaminate drinking water sources when management is inadequate and when protective measures fail to be enforced.

The incident in Walkerton occurred in May 2000 and was caused by a combination of physical, environmental and human factors. First, the water well was shallow (< 5 m depth), in highly fractured limestone, with little surface soil cover, and little natural filtering capacity. Manure was applied to agricultural land in the vicinity of the well in April using best management practice. In early May some 135 mm of rainfall occurred over a 5-day period and, due to the highly fractured bedrock, water contaminated with E.coli found its way into the well and the drinking water systems. A series of human failures occurred which included lack of chlorination, falsification o f reports, failure to report analytical results to the health authorities, and lack of government scrutiny in monitoring and enforcement that resulted in the tragedy (O'Conner, 2002). This incident shows that even when appropriate regulations are in place, water pollution and health problems can occur due to negligence, poor management, human errors, lack of enforcement of regulations and best management practices.

Managing drinking water is a complex process and there is often no consensus on what measures best protect water supplies. Everybody seems to have an opinion on this issue but there is generally a lack of knowledge and understanding of requirements to provide safe drinking water. It can be stated that there is no absolutely safe way of protecting drinking water for everybody at all times.

Water is a cyclic resource, moving through the hydrologic cycle. Water in the form of precipitation is naturally acidic and is more or less in equilibrium with carbon dioxide (carbonic acid). Natural precipitation reacts with vegetation and soil as it enters and flows through the canopy and soil matrix. If not lost through evapotranspiration, water moves laterally and vertically and in humid areas becomes groundwater or moves directly into streams and lakes. During this journey water dissolves minerals (nutrients) as it interacts with soils, vegetation, and the atmosphere and is also impacted by all land use activities. If conditions are appropriate, water may be charged with excess minerals or contaminants from human activities. Water with dissolved minerals is an ideal substance for biological and microbial growth. Thus one of the most challenging problems is microbial contamination and growth that can occur at the source or anywhere within the hydrological cycle or water delivery system. In the past we relied on chlorine as the most effective treatment method for bacterial contamination. This treatment has been questioned as being insufficient to deal with many viruses and protozoan (such as giaridia and cryptosporidium), and at the same time some people claim that chlorine itself poses a health hazard.

As a result of this concern, a multi-barrier approach is being advocated. This is a system approach that attempts to identify all sources of contamination in a watershed context. Sources are identified and corrective measures can then be taken that range from source control and creation of absorptive buffer zones, to water treatment, including ozonation, ultraviolet treatment and filtration through sand and membrane filters. …

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