Yes, insulating the pipe will help. However, insulation just slows down heat gain, it doesn't cool anything. So, if you have the cold water line sitting there in the attic all day with nothing running through the pipe, it will still get pretty warm after a number of hours, even with insulation. I don't know of any reasonable solution that will keep the cold water at a truly cold temperature when you have it running through your attic in your environment.

I had the opposite problem of copper pipes in my attic that could freeze in the winter: I went into the attic and laid the insulation batts over the pipes so they were essentially picking up heat from the house interior, rather than losing it to the cold air in the attic. If you have insulation batts, and you do the same thing, then the cold water pipes will tend to stay at the temperature of the interior of your house, rather than the hothouse of your attic. If you have blown in insulation, you could move it aside where the pipes are, place cardboard "tents" over the pipes, and then move the insulation back in place, but only on top of the tents. This allows the pipes to be more part of the interior and less part of the attic environment.

Sounds just like my hose that sits in the sun.

Use the grey polyethylene (foam) pipe wraps. A simple solution that will make a world of difference - at least you won't get hot, hot water at the beginning.

I had the same problem in San Diego. I usually just took a shower, just using the 'cold' water, before doing anything else needing cooler water. This was only convenient about 2/3 of the time, but was better than nothing

Cold Water Line Heats up in Hot Attic

Matter of normal course in TX. :-)

Definitely insulate the pipes. Also, do you have a return line for the hot water circulation? Or are you using the cold water line? If you are using the cold water line for the return, that may be part of the problem.

Thanks for everyone's great input. To answer a couple of questions, the hot water loop is separate from the cold water lines. It is insulated the entire way from one end of the house to the other. There is an electric pump next to the water heater that moves the hot water through the pipes, delivering hot water quickly to most any faucet.

The hot water in the cold water pipe is due to the hot attic. The weather has cooled significantly here in SoCal and I can tell the difference. Today was about 70 degrees, and the "cold" water comes out room temp instead of hot when we have the 100 degree days.

I know the problem. I was just wondering if there was an easy solution. Inslutating the cold pipe? Or the other one that makes sense - removing the insulation below the pipes, and tenting it over the pipes so maybe the air conditioned rooms below will keep the space with the pipes a bit cooler than when they are fully exposed. Or, just live with it. Maybe an under-sink chiller hooked up to the small filtered water faucet is in order.

An easy solution...

An insane idea...

You could pick up a water radiator, or have a shop make you a radiator... and hook this into the cold water line just before it exits the attic. A fan built onto the radiator - turning on and off by thermocouple. An extremely efficient cooler. This would cool the water down.

So would probably some insulation, and definitely an under-sink chiller. Sometimes I have insane ideas.

Appreciate your response on the recirc question.

"You could pick up a water radiator, or have a shop make you a radiator" -- I'd certainly have major concerns with an auto radiator (even a new one) or one fabricated about lead and other toxins.

An insane idea... Yes it is since it wont do anything but make the water perhaps hotter

Its not like the plumbing pipe was sitting in the sun, the heat making the cold water pipe is the ambient air around it in the attic which is exactly what you wish to blow over it. With the exception of any radiant heat from the roof that may be affecting it then yes insulation will help greatly.

Unless your drawing cooler air from outside to pass over that radiator or spraying water on it to create a cooling tower it won't work.

I had pecan Repipe done in my house and I saw where they were sending cold and hot pipes from a narrow holes specifically where some area that they had no other choice cold and hot in one side of my house about 70’ where next to each other that is why I don’t have a chill water and I called them back to see if there is anything they can do they gave me that explanation of hot attic but that is not the main reason.

I have turn off water heater since the end of June and still getting just hot water. Even if it runs none stop for 30 minutes