[KarlInOhio]

But if the now colder cold water must be mixed with more hot water to be usable for showering or clothes washing (the two biggest users of hot water) are you really gaining anything? Maybe you're using the original temperature water for the house and just flushing out the chilled water.

I know that I have to use warm water for washing because cold water (as defined for washing clothes) is around 85°F while the cold water from my pipes is below 50°F in the winter and may be up to 60°F in the summer. That's not washing or rinsing anything well. If I get a new washing machine that only has a cold rinse, I'll have to premix hot and cold water before it goes into the cold washer intake.

[douginthearmy]

But if the now colder cold water must be mixed with more hot water to be usable for showering or clothes washing (the two biggest users of hot water) are you really gaining anything?

First thing I thought of. I was scrolling down looking to see if anyone brought it up. They might get some gains by capturing some of that ambient heat in the pipe water, but I highly doubt their efficacy numbers. A good amount of that ambient heat will be lost by warming the now too cold tap water. The dish washing machine is about the only thing that uses the fully heated hot water.