Why is the water from my cold water taps warm?
If the cold tap is warm for a while and then cools back to normal, it is a real possibility that you have leak in the hot water line, under the slab. Overnight the hot water leak will beat up the area which includes (usally) the cold water pipe. Depending on where the leak is at, the cold water tap will be cold and then warm when first turned on and then cold again. This is called a slab leak. I have had three. It's almost always the hot line that leaks.