Concerns about DPG (diphenyl guanidine) by-product in drinking water

 Dear Mr Chen Ko,

I am a fan of reading your blog posts.  Thank you for doing such a great public service for sharing your knowledge.

I have a question.  Recently there is a Straits Times report about possible DPG-chlorine by-product in tap water:

https://www.straitstimes.com/singapore/local-scientists-studying-chemical-in-tap-water-to-determine-if-harmful-to-human-health

I am using a Berkey filtration system.  Do you know if a Berkey is able to filter out this DPG-chlorine by-product?  If not, are there any home based filtration system that can do that?

Thank you very much for your advice.

HA

 

Dear HA

Thanks for sharing the Straits Times article.

Here are my thoughts regarding the issue.

1. The first thing that struck me when reading the article was that the chemical substance in question, a by-product of the reaction between DPG and chlorine, was not identified. This is strange and I seriously cannot fathom why PUB did not release it (and ST not pursuing its identity).
    
2. In case you have not read the article, DPG is found in rubber products, including the rubber gaskets and seals used in our water distribution system. The article maintains that DPG can leach into our drinking water as water is conveyed from the water treatment plant to our homes.
   
   
3. As for chlorine, it is intentionally added into our drinking water for disinfection purposes at the water treatment plant. Apparently, chlorine and DPG can react in the water distribution system to form the unnamed by-product of potential concern.
   
   
4. The concern about chlorine and its by-products in drinking water has been raised for many years worldwide. Its continued use in municipal drinking water has always been justified by its benefits (keeping the water germ free) against its potential hazards. This is perhaps why the WHO limit for chlorine in drinking water is given at an amazingly high value of 5ppm (parts per million). Apparently, this value was chosen to avoid giving rise to water that tastes like the swimming pool, rather than to prevent any specific detriment to health.
   
   
5. DPG and its by-product are new to the drinking water scene. Their health effects and safety levels in drinking water are far from established. To me, this is shaky ground to justify for home water treatment as the facts are not strong to make a decision.
   
   
6. Nevertheless, I believe that the consumer is entitled to achieving peace of mind by trying to eliminate these substances in drinking water. With little data on the actual concentrations in tap water and probably zero data on any home water treatment device successfully removing them, I am going on a leap of faith to say that the best bet to remove them at home is a reverse osmosis (RO) unit. If you are concerned enough about your health to ask questions about DPG & its by-product, you are probably willing to spend some money to get a unit from a reputable supplier.
    
7. Interestingly, the news article mentioned that PUB's water treatment plants manage to remove these substances. RO is routinely used in its water treatment plants so that is perhaps a step in the right direction for home treatment.

Good luck!

 

Figure: A typical under-the-sink reverse osmosis (RO) unit

Descaling for home appliances?

 Also, what are the consequences if we don't descale - the iron, airpot works fine. 

For Nespresso, I read that they will take longer to heat or water will be cold, coffee will be bitter. 

They still heat up. 

How do I know if the 1) to 3 items need descaling?  

Thanks again. 

 

Thank you Mr Chen Ko for your thorough water blog. 

 

Hope you can advise me if the following needs regular descaling if used in Singapore with its soft water:

1) Iron with water container, 

2) Thermal air pot or  kettle 

3) Nesppresso?

 

So far we have not descale any of our electric water containers. 

At most, I  see the ageing water heating rod turned orange in our kettle.  

Thank you for your kind sharing. 

 

kim

 

Dear Kim

Here are a few thoughts regarding the issue.

1. Hardness in water is due mainly to calcium and magnesium initially dissolved in water. Due to heating, these calcium & magnesium react chemically with other substances in water to form your solid scale.
   
   
2. Toxicity of scale is not an issue so we can leave that out of the equation.
   
   
3. However, scale does adversely affect heat transfer in heating equipment so a thick layer of scale means that you need more power to heat up the same amount of water or beverage. In industry, it is a standard practice to descale large-scale heating equipment to minimise heating costs. For domestic purposes though, I hardly hear of such a practice as the economics probably do not work out favourably. Your equipment probably fails before the scaling becomes problematic.
   
   
4. As you rightly pointed out, the water in SG tap water is soft so the scaling problem is somewhat less severe than in other countries consuming hard water in their homes.
   
   
5. Though scale is somewhat stable normally, it can break up and dissolve in an acidic environment. Incidentally this is one way to perform descaling. You mention about coffee so yes, if your coffee has the right level of acidity (this applies to tea too), the scale can dissolve into your beverage and most likely affect its taste.
   
   
6. Long story short, if you believe the scale is affecting the taste of your normally superb coffee/tea, go ahead with descaling. However, I am unsure of the economics of such a move compared to simply getting a new machine.
   

Good luck!

Figure: Nespresso machine

 

The History of Water Quality in Singapore: Talking about Science from a Historical Perspective (or is it History from a Scientific Perspective)

[Appended in March 2024: The experience in 2023 had been so positive that I returned in March 2024 to give another round of training to the latest batch of docents of the National Museum of Singapore. The session was conducted more like a discussion rather than a lecture. This is one of my preferred modes of "training" for adult learners.]

 

I recently (March 2023) had the privilege to be invited to provide a training session to the docents of the National Museum of Singapore. The topic was on the history of water quality in Singapore. Admittedly, history has never been my forte since my secondary school days. In fact, I used to thumb my nose at the subject. However, water quality is and it has always been my pleasure to share about this topic with all manner of audience and even from a historical perspective.

Click here for the full video of the talk.

Click here for the full write-up of the talk.

 

Being Interviewed on Talking Point shown on Channel 5, Nov 2022: Is Bottled Water Worth Your Money?

Despite the title of this episode as given above, I was not sought for my views on bottled water. Instead, I gave my take on alkaline water which appeared in a segment in the middle of the show. In a nutshell, my stand has been consistent with what I have been saying on this blog all this while. (Check out an earlier post for a more in-depth discussion: Why I wouldn't be drinking alkaline (aka ionised) water.) There is much well deserved skepticism regarding alkaline water. Until these issues are cleared up, the claims regarding alkaline water continue to sound nebulous.