The water in the cold water lines is getting warm while it is standing. Perhaps the hot water lines are nearby and are warming the cold pipes by convection. Your cold water pipes may also be running through areas of the structure (walls, ceilings, attics, etc) that are warm. The only thing you can do is try to insulate the pipes (both hot and cold). Insulating hot water pipe is always a godd idea, as it saves energy.
» This message has been edited by nicktheplumber on 15 September 2003
This can happen if you have some plae where the hot and cold water are connected together. Some places could be a shower that you turn off at the shower head instead of at the shower valve. With both the hot and cold water on at the valve, the hot can flow into the cold water pipe when the shower is off. Or a shut off on a hose attached to a sink.