Even though the water pipes differ for the most part, the size of the water supply pipes to your fixtures would be the same for both hot and cold lines. Standard sinks and tubs would use 1/2" supply lines, and toilets use a single 3/8" line.Sep 29, 2015
What size is water heater copper pipe?
In some areas, Type M pipe isn't allowed for delivering potable water, but it can be used for hot-water heating systems. Copper pipe is commonly available in diameters ranging from ½ inch to 2 inches.