Water disinfection

The production of safe drinking water takes several steps to remove all kind of unwanted substance out of water. One important step is disinfection, i.e. killing (possible) pathogens in water.

One of the earliest disinfection methods, and which is still used in many countries, is water chlorination. The benefits are that it is an effective and cheap method. Water chlorination has saved the lives of millions of people.

Chlorination has, however, some disadvantages. So there is the possibility of chlorination by-products, i.e. chlorine might react with other substance in drinking water which might be hazardous. If chlorination is done properly, the risk posed by these by products is quite small.

Another and more important consequence of water chlorination is the effect on the taste and odor of water. Many people simply do not like the taste of chlorinated water. And instead of drinking tap water, many consumer prefer to buy and drink bottled water, which does not contain chlorine.

That people avoid tap water and use bottled water instead, is a serious concern. Most bottled water is sold in plastic bottles, which result in an enormous amount of plastic waste. It is obvious that this is a serious environmental concern.

If want people to drink tap water and to fill their bottles with tap water (rather than buying new bottles of water each time), it would be wise to provide chlorine-free tap water. Though this would require an alternative methods of drinking water disinfection than chlorination.

Ozone could be used as a disinfectant instead of chlorine. Since ozone leaves no residues (because its broken down to oxygen), it does not affect the taste or odor of tap water. Back side is that the residuals also means there is no further protection against contamination after drinking water has been pumped into the network.

Another alternative is UV disinfection. UV radiation kills pathogens as effectively as chlorine, but there are no residuals and hence no taste and odor effects. In order to guarantee continue protection against contamination, UV disinfection could be repeated throughout the system.

Of all these methods of water disinfection, UV disinfection is our preferred method.

Since we expect questions/remarks about water fluoridation, we shortly discuss this as well.

Unlike chlorination, water fluoridation is not intended as disinfection method but as an effective and cheap measure against tooth decay. Tooth decay is a serious medical condition and water fluoridation saves a lot of money in dental care, and is an excellent method of “dental care” to the less affluent parts of society.

Our opinion on water fluoridation is that it is actually unnecessary. The fluoridation of toothpaste has been proven to be an effective measure against tooth decay. Many European countries do not fluoridate water, but require the fluoridation of tooth paste.

There are all kind of whack critiques about water fluoridation, which you can find here.

water-bubbles

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6 thoughts on “Water disinfection”

  1. Another concern would be where the water comes from; if you’re expecting a high starting level of contamination, then more steps would be required. Filtration can be expensive but effective. Public water would typically be purified using several different treatments; it’s a good idea to use a low level of chlorine even after UV treatment to protect the water once it leaves the treatment facility. Alternatively, you could treat the water with a high level of chlorine and remove a significant portion before it leaves the facility.

    1. With modern filtration techniques and UV disinfection, there is really no need for adding chlorine to the water supply of space settlements. [it is not quite likely that water in space settlements will be highly contaminated with pathogens.]

      For instance in the Netherlands water chlorination is illegal, and yet water-borne disease is virtually unknown there.

      The only reason why many countries still use water chlorination is because it is easy and cheap.

      >>Alternatively, you could treat the water with a high level of chlorine and remove a significant portion before it leaves the facility.

      In that case you could consider ozone as disinfectant instead of chlorine, as ozone will be broken up naturally.

      1. I’m assuming that most of the water would be coming from human waste (in the interest of sustainability)? That would definitely lead to high pathogen contamination, or at least faecal bacteria which can be pathogens in some people and commensals in others.

        1. In closed circuit we have still two separate steps: waste water treatment and making tap water. If the first step is done properly, there is no need for any adding chlorine in the second. Once all pathogens present in the waste water have been destroyed, by whatever method, they are gone.

          Of course, it is important that tap water and waste water are not mixed at any point in the tube system. But that’s an easy problem to solve.

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