Understanding Water supply pipes and fittings

Water supply pipes are usually made of galvanized steel or copper. New drain lines are almost all made of plastic, either polyvinal chloride (PVC) or acrylonitrile butadiene styrene (ABS); these two can be added to cast-iron drains.

Natural gas lines are almost always made of black steel pipe and are installed the same way as galvanized steel pipe. It’s important to check for leaks in these pipes. To do so, pour soapy water o the fitting and look for small bubbles around the joint.

To choose the right size of pipes you want to make sure that you measure. It’s important to buy the correct size pipe. Pipes are sized according to the inside diameter.

To measure a pipe from the outside, wrap a string around it and measure the string. To figure the inside diameter for copper pipe, subtract 1/8 inch; for cast iron pipe subtract ¼ inch; and for plastic pipes subtract 3/8 inch.

The most common sizes for residential pipes are:

Main water line – ¾ or 1 inch
Water supply lines – ½ or ¾ inch
main stacks – 3 or 4 inches
Kitchen sinks and tub – 1 ½ inches
Bathroom sinks – 1 ¼ inches

Always measure twice because detail measuring for pipes will save you time and money.

Master Faucet Products Installation Guide