Tap Water Temperature Vs. Time

I had always thought that tap water had the same temperature year-round since the pipes were buried in the part of the ground where the temperature is constant. Much to my surprise, I found the temperature of the water from FPUD varied tremendously over the year:

To measure the water temperature, I first allowed enough water to flow from my faucet (used in watering) so that the water was coming from the water main in the street. I then filled a bucket with water and measured the temperature. The measurements in the plot above were taken beginning in July 1998, and you can see the close agreement between July 1998 and July 1999.

What must be happening is that the water never has enough time to sit in the distribution pipes long enough to acquire the average below-ground temperature of Fallbrook. Instead, the temperature must be determined either by the reservoirs in Fallbrook, or by the temperature of Lake Skinner, where most of our water comes from. In the future, I plan to compare these observed temperatures with average Fallbrook temperatures and average Lake Skinner temperatures to see which influences the observed temperature the most.

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Copyright © 1999 by Tom Chester.
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Last update: 17 August 1999.