When you turn on a tap you expect crystal clear water to run out.   But does it?  While the water may look clear, how often have you been able to smell the chlorine that has been used to treat it?  Obviously this affects the taste not just of your drinking water, but also your tea, coffee and anything that is cooked using that water.   Water is a great solvent and in the course of getting from the clouds to your tap, it may absorb or carry a number of contaminants.

Water contamination can occur in a variety of ways.     There are environmental contaminants such as dust, ash (e.g., from bushfires), animal waste, parasites and bacteria (e.g., giardia, cryptosporidium, and E. coli).  There are commercial contaminants such as herbicides, pesticides, fertilisers and industrial waste.  These can find their way into the water supply through run-off, leaching into groundwater supplies, or through accidents (e.g., overturned chemical tankers, industrial waste treatment malfunctions).  Additionally, there are contaminants added by the water supply authorities, ironically, to make the water "safer" to drink.   These additives can lead to disinfection by-products.

Effects of Contaminants

Dust and Ash

At the very least, dust and ash cause turbidity in the water, thus the water looks cloudy or muddy.  Depending on the type of dust or ash this may not be a problem in itself; however, turbidity may interfere with the disinfection process and possibly provide a medium for bacterial growth.  It certainly makes the water look unappealing and can also adversely affect the taste.

Animal Waste, Parasites and Bacteria

Animal wastes in water supplies can lead to dangerous levels of faecal coliform and E. coli bacteria.  Giardia and cryptosporidium are parasites that may enter the water supply through sewage and animal wastes.  These bacteria and parasites can produce symptoms of cramps, nausea, diarrhea, fever, fatigue, and vomiting.  In the case of people with weakened immune systems, the symptoms may be more severe and can  even lead to death. 

Herbicides, Pesticides and Fertilisers

These enter the water catchment primarily through run-off or accident.  Even where they may not have been used for years they may still be present in the soil to be leached out and enter streams feeding into catchments.  Accidents when conducting aerial spraying can also lead to contamination (see, for example, Stateline).  Contact with these may lead to nausea, vomiting, Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, learning and/or behavioural disorders, infertility or other reproductive problems, increased cancer risk.

Deliberately Added Contaminants

Water treatment typically involves coagulation, flocculation and sedimentation.  Water Supply authorities are permitted to use up to 50 different chemicals to clarify and disinfect the water.  The chemical most people are aware of is chlorine.  This helps to kill disease causing organisms in the water.  The problem is that some organisms are resistant to chlorine while a further problem is that chlorine reacts with organic matter in the water to produce trihalomethanes (THM).  Several scientific studies have shown the possible link between THMs and a variety of cancers.

The flocculation agent aluminium sulfate is added to water to cause suspended particles to form into bigger particles and settle out of the water, thus clarifying it.  However, aluminium has been linked to Alzheimers disease and other problems (see, for example, Report on UK ALuminium Incident  ).