We’re told many myths these days, but the truth be told clean drinking water is a very scarce commodity.
By the early 1900s, rates of waterborne disease were greatly reduced in developed nations through better protection of water supplies from sewage pollution and simple but effective methods of water treatment, such as sand filtration. The widespread introduction of disinfection in the early twentieth century improved public health even further.
However, waterborne diseases continue to be a major cause of illness and death in many parts of the world, where more than one billion people drink unsafe water. The World Health Organization (WHO) estimates that each year 2.4 million deaths are caused by unsafe water and lack of sanitation. Yes, even in Australia – the Lucky Country.
‘Bugs’ in the Water
Ever heard of Microorganisms? You’ll never see one but they are capable of causing disease are called pathogens and include bacteria, viruses, and protozoa such as Cryptosporidium and Giardia. And they live in your water.
In drinking water supplies, the pathogens of concern are mainly those found in feces of humans or animals.
Pathogens of human origin are generally regarded as the greatest health risk from water supplies, as many of the significant water-borne diseases, such as cholera and typhoid, are found only in humans. If present in a water supply and not removed by treatment, these pathogens can cause infection in people who drink the water.
However, some pathogens carried by animals can also cause illness in humans. When such illnesses are waterborne, their most common source is mammals in water catchments (whether native, feral, or agricultural) and birds in service reservoirs.
Coagulation, Flocculation and Sedimentation
Now what are these things we hear you ask?
While many particles will gradually settle out from water over time, (a process called sedimentation), some will not. To cause slow or non-settling particles to settle out more readily, a soluble chemical or mixture of chemicals is added to the water. Such chemicals are called coagulants and the process is called coagulation.
Coagulants react with the particles in the water, forming larger particles called flocs, which settle rapidly and can be removed as sludge. Flocs can also be effectively removed by passing the water through a filter; either directly or after sedimentation. The process is controlled so that the coagulant chemicals are removed along with the contaminants.
These processes remove some of the natural organic matter that is washed from soil and vegetation as water travels across the landscape. Natural organic matter is usually the cause of brown discoloration in water and can also cause foul tastes and odours. However, not all of this natural organic matter is removed by coagulation and it may react with disinfectants applied to the water, to form disinfection by-products.