ABSTRACT
Public supplies, those provided by large utilities, water undertakers, municipalities or private companies usually provide drinking-water that is of uniformly good quality and which is getting better all the time. Small or private water supplies, in contrast, are often of dubious quality and will probably remain so for a considerable while. Even within this category, domestic supplies are five times more frequently contaminated than commercial water sources and the smaller the supply is, the more likely it is to be contaminated (Rutter et al., 2000). For a variety of reasons, water from small sources can periodically contain microbiological contamination, dissolved metals, various organic chemicals and small particulate matter. This may have been washed off the surface of the land or dissolved from the soil or the rock the water passes through. The water will also have physical properties such as acidity and hardness that depend on the surrounding geology. Most urban dweller can rely on their tap water being cheap and safe to drink. For those adventurous souls who live in or visit remote rural areas, a simple glass of water may contain organisms that can make them ill, or in the case of E. coli O157 may kill them. This is not to say that you will become ill as soon as you swallow that refreshing glass of water or that farmers are dying in droves from their well water. The human body will build up immunity over the years to provide a measure of protection and the quality of private water supplies varies a great deal according to the weather, so you may be lucky.
