Propylene Glycol as a water main anti-freeze

Question

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?

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.