Rainwater running to waste with no gutters to collect it.

Post-chlorination concerns the management of water before it leaves the treatment plant and then following its course in the reticulation system. It is part of a discussion on the harvesting of rainwater and storing it in relatively small private underground reservoirs holding in the region of 30 kilolitres.

Chlorination of our drinking water is arguably one of the greatest breakthroughs in public health; cholera and typhoid deaths, and other waterborne diseases have virtually been eliminated in the developed world.

It has another great benefit over other means of disinfecting public drinking water; there is a residual effect that continues in the reticulation, destroying bacterial pathogens.

Yet still today over three million young children die every year in the developing world from bugs where proper reticulation and sanitisation of water does not exist. 

With the new realisation that the healthy bacteria in the gut play an extremely important role in the prevention of non-communicable diseases, questions are being asked whether this residual effect of chlorine may have a low level antibiotic effect on the so-called microbiome that lives in the gastrointestinal tract of humans[1].

Numerous animal studies suggest that at the levels of chlorine in our drinking water it is safe; perhaps reasonably safe would be better said. However, there are no studies to date that evaluate the possible toxic effect of that residual chlorine on the microbiome that inhabits the gut.

Since the contents of the stomach are already highly chlorinated, it is unlikely that any ingested residues would have much of an effect.

Of even greater concern though is the effect of chlorine in our water reticulation on organic material forming toxic trihalomethanes (THMs) that cause bladder cancer and other problems like miscarriage.

You may have read in the media that Cape Town’s water currently has an earthy taste; it is due to high levels of organic material from the Voëlvlei Dam. Despite assurances from the authorities that it is safe to drink, residents are rightly concerned.

These findings, plus the large amount of plastic micro-particles in our drinking water, create great difficulties for those concerned about their wellness. Are we becoming neurotic, on the verge of what is known as orthorexia?

It is a pathological concern about right eating and drinking; a first cousin to its better known cousin anorexia.

For me it is just one more reason we are so pleased to have built an underground reservoir which stores our rainwater; that will certainly have some organic material from the gutters but, in the absence of chlorine, no THMs are formed. We have a happier microbiome and there is the certainty of no plastic being ingested. There is little or no risk of waterborne bacteria like E.Coli or cholera, and even amoeba from faecal material, but it would be safer to boil the water that one intends to drink.

The photograph above for me is one of the prime reasons our cities are running out of water; where are the gutters?

The first step for the greenie wanting to get off the chlorinated municipal supply is to install gutters. Research indicates that 8 percent would have found its way into a river and been harvested, but the vast majority is just wasted either through evaporation or runoff; tragic in a dry and thirsty land such as ours.  

Chlorine dioxide

Chlorine dioxide is sometimes used to kill microbes in water because unlike the straight gas it does not generate trihalomethanes that have been shown to cause serious tumours in the presence of humic substances.

However, various authors have shown that chlorine dioxide does affect red blood cells and the ability to turn T3 to T4 in the thyroid gland, due to the inhibition of iodine[2].

The initial rate of iodide influx is inhibited up to 98% by the chloride channel blockers.

In a similar manner, fluoride from drinking water has a similar toxic effect on thyroid hormones[3]. The authors recommend water purification such as reversed osmosis in home; we punt rather for drinking natural rainwater so you don't lose out on the minerals. In short post chlorination is a complex subject.


Post-chlorination raises issues about the possible effect of toxic chemicals on the microbiome and the advantages of collection and storage of rain underground. The transition to our modern era has brought huge benefits to humans in terms of clean water but at the cost of ecological disturbance of our internal environment, generally known as dysbiosis.

There is strong research that the loss of biodiversity of the microbes in the human gut is closely allied with asthma, atopic dermatitis and chronic non-communicable diseases.

The completed underground rainwater reservoir that requires no chlorine for sterilisation.


There are many studies confirming that the fluoride added to water to lessen tooth decay also increases the risk of bone fractures, especially of the hip.

We lie between the devil and the deep blue sea; a lifetime of compromises. I would prefer to avoid both post chlorination and fluoride treatment by using harvested rainwater, and protect my teeth by using bicarb both as a deodorant and for cleaning the fangs.

For the busy active outdoor person fluoride is most likely not a problem, but for those who are stuck inside it may just be one more nail in the coffin.

One gets fluoride not just from the municipal water, of course; it's also in tea and coffee. Drinking excessive amounts adds to the toxic effect of fluoride.

Decaf remains highly controversial incidentally. The caffeine is generally removed using an organic solvent such as dichloromethane, some residues remaining in the coffee.

  1. Bernard Preston
  2. Rainwater harvesting model
  3. Post-chlorination
  1. The Effects of Chlorinated Drinking Water on the Assembly of the Intestinal Microbiome
  2. Subchronic toxicity of chlorine dioxide in drinking water
  3. Impact of Drinking Water Fluoride on Human Thyroid Hormones


Our newsletter is entitled "create a cyan zone" at your home, preserving both yourself, your family and friends, and Mother Earth for future generations. We promise not to spam you with daily emails promoting various products. You may get an occasional nudge to buy one of my books!

Here are the back issues.

  • Wear your clothes out
  • Comfort foods
  • Create a bee-friendly environment
  • Go to bed slightly hungry
  • Keep bees
  • Blue zone folk are religious
  • Reduce plastic waste
  • Family is important
  • What can go in compost?
  • Grow broad beans for longevity
  • Harvest and store sunshine
  • Blue zone exercise
  • Harvest and store your rainwater
  • Create a cyan zone at your home

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South Africa