Re: Why is water from faucet cold then warm then cold?

On Sunday, February 20, 2000 at 2:00:00 AM UTC-6, Authenticator wrote:

Hi Authenticator,
This is happening now to me now that I've moved to Alabama? Do you live in the South, too?
Alabama Yankee
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snipped-for-privacy@gmail.com pretended :

Be prepared to wait *another* sixteen years for a reply.
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On Sun, 07 Aug 2016 23:41:38 -0400, FromTheRafters wrote:

The answer to the original question is easy. The CW pipe feeding the HW tank warms up for a good distance both up & downstream from the "T" feeding the HW tank.
The pipe further downstream near the faucet is closer to ambient temperature. This is the first water to exit the faucet. It is followed by the water that was resting in the pipe near the HW tank which is warmer. That is followed by fresh water that just came in from the pipe undergroung feeding the house. Usually this will be cooler than the initial flow.
This does remind me of something from my days in college. There were a few of us renting an apartment at a place everyone called "Cockroach Towers" on the 9th floor.
If you turned on the cold water and let it run, it would normally never get very cold at all. Basically, by the time the water got to our floor, it would be at about ambient temperature of the air in the riser. In the summer it would be only slightly cooler than tepid no matter how long the faucet had been open.
It was under pretty good pressure though. We were close to the water tower, and it took all the strength of one thumb covering the other to staunch the flow.
I discovered this when I was experimenting with how to target anyone passing into the kitchen with a directed dousing. When I tried to increase the pressure by opening the hot water control, I noticed something truly remarkable:
With both taps open, if a stream was allowed to flow under pressure (i.e. partly blocked; not free-flowing), then completely stopped off for a few seconds, and then released a bit to let out a high pressure stream, after a few seconds of lukewarm water, there was a blast of frigid teeth-chattering almost ice-cold water, followed again by the lukewarm water. We all soon became adept at repeatedly blocking, releasing, and collecting the cold water. An average size drinking glass needed about 4 or 5 cycles.
Nobody ever figured out the mechanism for the cooling. Each apartment had its own 10 gallon hot water tank, which I believe had a 'vacuum breaker' installed.
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