If I am correct, my plumbing works as follows:
[ul]
[li]A water main brings water from the city’s supply into my house.[/li][li]That water breaks into two lines: designated Hot and Cold.[/li][li]The Hot Line heads through my water heater then into the various fixtures in my home.[/li][li]The Cold Line heads straight to the cold supply side of the various fixtures.[/li][/ul]
If that’s the case, what makes the cold water… er… cold? I mean, is it just me, or is it true that the longer you let the cold water run, the cooler it gets?
If it is really hot out, does the sun make my supply pipes so hot that even my cold water is warm? (I think this happened in my school in Israel - on hot days, you couldn’t take a cold shower because the supply pipes were buried too shallow.)
In warm climates, what makes the cold water cold? Is there a Water Cooler somewhere that cools the water for the city? Do Los Angelenos have to buy an extra appliance - one to make their water cold?
What gives?
Well, most water is delivered underground and, depending on latitude, underground temperatures are about 40-60 degrees F. (If you live in Canada or Alaska, winter temperatures may require freezing prevention.) This stable subsurface temperature keeps the unheated water unheated. Usually. The last few yards of pipe may get some solar heating in the summer, but it clears out in a matter of seconds.
(In the hot summers in Colorado, we’d go hiking and find cool caves to lounge in behind the fountain sandstone cliffs - the rock was like a natural air conditioner.)
Here in Pasadena (suburb of Los Angeles) the water in the summertime doesn’t need to be cooled. However the pipes that lead from the outside of my apartment to my cold water taps are on the west side of the house, while the pipes from my hot water heater to my taps are run internally.
Which all means in the afternoon and early evenings, when I open a cold tap, it runs warm for a minute. But when I open a hot tap, it runs cold for a moment.
Although I am a physician, I used to be a plumber. In fact, I paid my way through med school by working in that trade.
Most urban homes have a single line (1/2"-3/4") that brings cold water from the municipal supply into the home. This line is split so that 1/2 of the supply continues on as “cold water,” and the other 1/2 goes into the water heater to provide hot water to the various plumbing fixtures and appliances (sinks, bathtubs, clothes washers, etc) that require hot water.
As regards the “coldness” of the supplied water, it is almost always the case that the deep supply lines to the house have the coldest water. Except in certain areas where the house plumbing is exposed to freezing temperatures. Thus, except in these very cold places, the cold water faucet is likely to release water that is warmer than the deep supply, and running the water for a while will eventually yield cooler water.