Disinfection – Making Our Water Safe


By Pete Scales, M. Ag BSc (hon)


In this modern age, in thriving communities, in developed countries, so many things in our lives are taken for granted.  Case in point: safe and abundant drinking water.

Safe and dare I say, abundant drinking water is generally considered the responsibility of municipalities and/or regional authorities, which in turn hold to quality and heath standards set at the provincial, federal and, increasingly, international levels. At a minimum, every civic authority must access, supply, remove sediment (clarify), disinfect, filter, and distribute drinking water to thirsty constituents and supply water for fire protection. Additionally, they are often held responsible to provide water for industry, agriculture and in some cases, surrounding communities.

Supply and distribution, accomplished to varying degrees since Roman times, are perhaps the easiest aspects of the drinking water equation – achieved by good old fashioned engineering. However, insuring that drinking water is clean and free of dangerous microbes is relatively new. In particular, disinfection, the act of effectively killing and rendering harmless dangerous microbes, was only accomplished on a grand scale just over one hundred years ago in Sweden with the identification of the element, Chlorine and its interesting cleansing properties, cities in Europe and then soon after, North America, started introducing it into water supplies. The effects on human health have been nothing less than phenomenal.  Deaths in the range of 250 per one hundred thousand due to typhoid, cholera, E coli and a number of the usual suspects, dropped off precipitously.

In order to be deemed acceptable to world standards and tight municipal budgetary constraints, water disinfection, only one part of a water cleansing strategy, must kill or neutralize essentially all pathogens in the water. 98% or greater kill rates are common targets. Disinfection needs to be automatic, easily and inexpensively maintained, relatively safe and above all, effective. An ideal system treats all the water for drinking, fire prevention, industrial and agricultural needs, and provides residual (long term) disinfection. So far the only disinfection methodology that comes even close to meeting these criteria is Chlorine, more commonly known as bleach.

Disinfection, including boiling of water, the increasingly popular ultra violet (UV) treatment, ozone treatment, and the most popular, chlorination, all work on microbial “baddies” including bacterial, viral, protozoan, etc., by disruption and destruction of their outer protective coatings. In the case of Chlorine, it is believed to create blister-like holes which allow the chemical to get inside the cell disrupting DNA formation, energy production and in relatively short order, killing the target microbes. It can take upwards of ½ hour of Chlorine exposure to achieve this “kill” effect.

Unfortunately, Chlorine with all its great disinfection capabilities, does not kill all microbes, particularly, those with tough outer skins such as cryptosporidium, and “baddies” like it that form spores and hard capsules. These microbes need to be filtered out by screens or by reverse osmosis.

And finally, if chlorination’s effectiveness against microbes is so good, the question has to be asked, “What is it doing to human cells once we drink it?” And the answer, thankfully, is that human cells are seldom found as single cells, like microbes, but as grouped cells, such as tissues and the sheer numbers of cells tend to provide protection. It is also important to recognise that the concentrations of Chlorine required to kill a single microbe cell are well within the safe limits for human health.  The only significant issue that research points out is the taste of bleach in our cups.

To better understand the effectiveness of Chlorine as a disinfectant in our water systems check out: http://www.scientificamerican.com/article/how-does-chlorine-added-t-1998-05-04/

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