We are a young student science group looking for solutions to real world problems. We are currently working on ways to keep our city water mains from freezing in the winter. Our team is researching adding propylene glycol to the city water supply in the winter when the weather forecast is really cold and could freeze older water mains (approximately -20 degrees F). Our older water mains are not deep enough to provide adequate protection against freezing and it is too costly to replace them all.

  • How much and what kind of food grade propylene glycol we need to add per gallon to keep the mains from freezing (or how to calculate it)? The city uses about 10,000 gallons of water per day.

  • When would we need to add it to keep the mains from freezing? We don't want to add it to the water if it's not needed.

  • How easy it is to dissolve and will it stay dissolved for at least 24 hours?

  • Will it interact with what the city already adds to the water supply, chlorine, polyphosphate and fluoride?

  • 3
    $\begingroup$ You'd have to add too much propylene glycol (50-50 mix with water) to protect to -20 F for this method to be practical. Also the public would go nuts with so much of a "contaminate" in the water supply. It would be a mess to flush out too. ref: ttequip.com/knowledgelibrary/… $\endgroup$
    – MaxW
    Oct 2, 2017 at 20:06
  • $\begingroup$ I think you might want to look at the pumping system, if you can keep the velocity high the water won't be able to freeze. You'll have lower water pressure though. $\endgroup$
    – J. Ari
    Jan 15, 2018 at 15:21

1 Answer 1


Picture this: Bob decides to boil some noodles. He fills a pan and places it on his stove top with the heat on high (since he is in a hurry). Then his phone rings and its the neighbor calling to say his dog has gotten loose. He runs out looking for his dog. While he is searching, the water has boiled away, leaving the propylene glycol heating. It bursts into flame, the kitchen and then the entire house is engulfed, his two year old daughter sleeping upstairs is burned to death.

Your "solution" is worse than the problem. The most obvious other problem with your idea is that for some odd reason (I can't explain it, because it is contrary to what your group must observe every day!!) you think water temperature and air temperature are directly related (or the same??). They are not. A simple search for "freezing point depression of propylene glycol" would give you plenty of information. Water use per day (in the USA) is about 80 to 100 gallons per person. That means your "city" has a population of 100. (????!!!!).

Other problems with your idea include washing your car - leaving a sticky residue which obscures your vision and leads to an increase in fatal traffic accidents. Killing your lawn (do you really think spraying PG onto your lawn won't have serious consequences.). And that doesn't even get to the various industrial uses of water which couldn't tolerate such adulteration.

Finally, PG is a food for bacteria. Do you really want to grow bacteria in your "water"? Or how about this, you wash your car, the water runs into the street. A car driving by attempts to stop for a stop sign, unfortunately you've lubricated the street with PG and a fatal traffic accident ensues. Below the Frost Line ground doesn't drop below 0°C. The deepest Frost Line in the Continental USA is 8 ft. It would be difficult to understand why your city's water pipes weren't placed well below this depth to begin with.

  • $\begingroup$ Thank you so much. You must be so proud of yourself for insulting a bunch of children literally in grade school and their parents (ie their coaches who are not chemists (I have an electrical engineering degree not chemical engineering)) trying to find solutions for real world problems while teaching the kids about science. So, we posted the kids' ideas and what questions we were trying to answer for our project only to be belittled by you. Pat yourself on the back. $\endgroup$ Oct 4, 2017 at 3:06
  • $\begingroup$ Not to mention you clearly didn't read the entire post. They were only looking to use PG DURING THE WINTER, not only that but only when it would be horribly cold! So, no, we wouldn't be putting PG on the lawn or washing our vehicles when the outside temperature is below -10F. Unless your pranking someone I guess in which case they wouldn't be able to use their vehicle for probably the rest of the winter. $\endgroup$ Oct 4, 2017 at 3:07
  • $\begingroup$ We obtained our daily city usage information from the city workers who actually work for the city water works. Not sure why you felt compelled to insult the children for that one! And I'm not sure where you live, but our city is about 200 years old and just 3 years ago they pulled up some of the first water mains that were put in (not below the frost line mind you because 200 years they didn't get the memo) and those mains were made of .......wait for it.......wood. $\endgroup$ Oct 4, 2017 at 3:07
  • $\begingroup$ So, I'm gonna go with they really didn't understand water distribution and what that all entails 200 years ago as we know it today. But hey, you just had to insult our city's founders while you were insulting children. Lastly, PG is in everything from drugs to shampoo. Maybe you should run around and tell all the companies that use it that they are horrible for putting something that breeds bacteria in our medication. I'm sure you will get award for that one. $\endgroup$ Oct 4, 2017 at 3:08
  • $\begingroup$ You know, you could have just nicely explained what the errors were with the idea and maybe, i don't know, have helped us think it through instead of being a jerk. $\endgroup$ Oct 4, 2017 at 3:08

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