Residential Plumbing Explained

Pipes, Drains, Water Supply and More

Cam Allen L.I.W. NHI

May 13, 2026

In this weekly Q&A column, retired builder/building inspector Cam Allen answers readers’ home renovation questions. Have a question? Enter it in the form below.

I chuckled a few weeks ago when I got this question “Why do plumbers always look stressed out?” I had a plumber I know quite well at our home recently helping me replace an awkward shower enclosure set and I asked him. He laughed too.

His response was cute, “What would you think if your job was cleaning up peoples s— for a living”. He went on to say that of all the licensed trades, the shortage of plumbers is the most acute. It’s because of this perception, even though it’s a vital, decent paying trade.

This week we will cover some basic terms, things you should know, along with a bit of related plumbing history.

Water Line Shut-offs

Depending upon where you live in the country, the very first thing you should know is where the main water line shut-off is located.

The next thing to know is the location of other secondary shut-offs. Every toilet has one – it’s located under the tank attached to the supply line at the back of your toilet.

Most modern homes also have shut-offs for the sinks in the kitchen and bathrooms. Familiarize yourself as to the location and type of shut-off present. Older homes often lack secondary shut-offs so when you upgrade any taps, add these.

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Water Supply

Home potable water supply breaks down to two parts, the supply water and the wastewater. You will hear two wastewater terms: greywater and blackwater. Greywater is the wastewater you discharge from your sinks; blackwater is the wastewater from your toilets. Your supply water enters your home from one line and then is divided off into potable water with a line going to your hot water tank.

Water Pipes

Before WW2 most water supply lines were galvanized and some were lead pipes. Copper pipe goes back to the Egyptians but it was only in the late 1920s when a method to produce thin wall copper pipe was invented that it became the standard for the next 60+ years.

During the early 80s we saw plastic pipes enter the market. One kind was called “Poly-B” and it quickly developed joint and integrity issues that resulted in some serious lawsuits. This pipe is light grey in colour and if you find it in your home, it should be checked for integrity. It was gone from use by the 80s and replaced by another type of plastic pipe called CPVC. This plastic pipe is a milky white colour and was more successful, though it did have some early joint issues. It is rigid and ample hangers were recommended.

PEX plastic pipe was introduced in Europe during the late 60s, then in the 90s its use grew in North America and it ended up becoming the supply pipe of choice. Today PEX, which stands for cross-linked polyethylene, is used in most residential applications due to its cost and faster installation time. The PEX pipe used today has few issues, is flexible, can be run with limited hangers and with two kinds of joint clamp systems. This is where most issues happen. I admit to a preference for the stainless steel clamps method for rust resistance and ease of use. I have never had one leak. PEX comes in colours: white for general use, red for hot water and blue for cold.

Water Testing

One small tip for my rural readers – get your water tested annually. The earth is changing and I have seen more and more rural homes where their well water has picked up some kind of contamination. A couple of months ago I was retrofitting a friend’s well supply with a 5-stage whole house filter system including a UV light on a well that for years tested clear.

Drains

Now we look at the other side of plumbing, your drains. This is the part my plumber friend Adam said is the “really messy” side of the business. Your toilet discharges blackwater and your sinks greywater. They all drain to one main sewage drain. This then empties into your septic tank if you live in a rural home or your municipal sewage system in a city.

These drains work by gravity, along with traps under your fixtures that hold some water and prevent sewer gases from entering your home. These traps, often black plastic or chrome metal pipes, are known as “P” traps. There are traps called “S” traps which are not recommended since they are known to “siphon” out the water, allowing sewer gases to enter the home.

Once this water leaves your sink it flows to a main stack pipe. This vertical pipe
extends from your roof to the sewage or septic discharge. You will see it as that black pipe sticking out your roof 18” or so. This pipe maintains atmospheric pressure within the pipes and prevents siphoning. One area where drains can be frustrating is where they connect to the main drain.

Known as an “air admittance valve” or to a plumber, “cheater vent,” these in-line vents sense the presence of air pressure created by the water pressure flowing through your drain, open a rubber flap in the vent allowing air to escape. This allows the water in the drain to flow down to the main drain. They are commonly used in kitchen islands and in an older home during plumbing renovations where access to the main stack is not reasonably accessible.

Most drains today are made of Acrylonitrile Butadiene Styrene or ABS black plastic pipe as it is called. These 3 chemicals are blended together in a mould to create a smooth, strong, rigid and impact-resistant pipe. Your main drain is usually 4 inches in diameter. Sinks are 1.5”, showers 2” and toilets are 3” drains.

Early drains were cast iron and lead pipe. It was in the early 1970s that ABS black plastic pipe took over, mainly due to cost and ease of installation. The one drawback to ABS pipes is they can be noisy and I have seen some custom homes recently where cast iron drains have been used instead of ABS.
There are other areas where ABS has become known for issues. The major one being if kept outside in storage where the ultraviolet rays of the sun could get at it, this pipe will rapidly deteriorate. It is also known to be susceptible to repeated high temperatures, like the discharge of water from a dishwasher
over an extended period of time.

We are now seeing the use of polyvinyl chloride drain pipe, known as PVC. This drain pipe is white, offers a quieter operation and is not as susceptible to high temperatures. Depending upon where you live in Canada, some locations do not permit the use of PVC as yet. One reason is ABS uses a one-step gluing method while PVC requires a careful two-step gluing process. I have known Adam, my plumber friend for a number of years and one thing he does say: plumbing systems today that are properly installed are more water cost efficient and reliable than ever.

Images from Depositphotos