Water supply lines: what exactly do they do?

July 15, 2016

Whether you’re repairing a leaky faucet or preparing to install a new sink or toilet, water supply lines are going to come into play. Here are some tips and tools you can use to successfully complete your DIY household plumbing projects.

Water supply lines: what exactly do they do?

Time: N/A
Frequency: As required
Difficulty: Easy to moderate
Tools: water supply line, wrenches, tape measure

What do water supply lines do?

So you know you need to purchase a water supply line, but what exactly is it?

  • A water supply line is the tube that connects a water shut-off valve to the bottom of a fixture, such as a faucet or toilet.
  • It brings water from your home’s permanently installed pipes to such fixtures and appliances as sinks, toilets, icemakers, dishwashers and washing machines.
  • Over time, supply lines may begin to rust/corrode or their nuts may loosen, causing leaking around your sink or toilet. It’s a good idea to replace your supply lines when you notice this.

Good to know!
For your safety and convenience, always shut off the water before you work with the supply line.

Types of water supply lines

Now that you know what supply lines do, it’s time to learn about the different materials they come in. Some of the most common you’ll come across are:

Flexible supply lines:

  • Often have a braided stainless steel or PVC exterior and inner PVC core for excellent corrosion-resistance and strength.
  • Easy to install. They’re ready to use with no flaring, cutting or bending needed.
  • They come with factory-installed ends in place so you have everything you need for installation.

Brass or copper supply lines:

  • They’ve been around the longest and offer long-life expectancy and reliability. Also, they often match the existing plumbing.
  • More difficult to install than flexible supply lines. You need to bend and cut them to length, which can cause kinking and render them useless. Also, they’re prone to corroding over time.
  • In older homes, they may contain lead-based solder.

Plastic supply lines:

  • Least expensive type of supply line.
  • Lightweight, corrosion-resistant and easier to install than copper.
  • Can warp at high temperatures, crack if frozen or may not be suitable for drinking water, so make sure to research the type best suited for your fixture.
  • Different plastics offer varying levels of flexibility and ease of installation.

Good to know!
Make sure to check local building code regulations for any restrictions on water supply-line materials in your area. Some areas restrict the use of certain types of plastic products.

Selecting the correct size

Supply lines come in many sizes and length combinations. To select the correct one for your fixture, use the following steps as a guideline.

  • Determine the length you need by measuring the distance from the inlet valve to the fixture.
  • Select a supply line that’s a little longer than your measurement so you have some room to work with.

Fitting size:

  • Select the fitting size for the type of fixture you are working with (faucet, toilet, dishwasher) as end sizes differ.
  • As an example, most toilet supply lines have a 9.5-millimetre (3/8-inch) compression fitting at the shut-off valve and a 22-millimetre (7/8-inch) fitting at the toilet tank.

Good to know!
For repair jobs, it’s handy to bring your old supply line to the store as a reference for buying the new one.

Handy installation tips

  • Buy a supply line with a metal nut or a reinforced plastic compression nut. Inexpensive plastic nuts will often leak or crack when tightened.
  • Don’t rush when attaching the supply lines. The threads can easily be stripped if the coupling nut is put on unevenly. Hand-tighten the nut first to ensure it’s going on straight.
  • For flexible supply lines, use two wrenches when tightening fittings. It’s always a good idea to hold against fittings when tightening or removing so that you don’t turn parts that you don’t want to move.
  • Always begin with new supply lines if you’re installing a new fixture. Even if the existing one looks fine, the rubber gasket may no longer be watertight.

Good to know!
Often, a leak is coming from one of the supply line’s fittings, which may have loosened over time. Before replacing a supply line, try tightening the nuts to see if it resolves the issue.

Now that you know more about supply lines, you can take the mystery out of leaky faucets and plumbing fixture installations with your DIY prowess. Armed with the proper tools, some knowledge and a little elbow grease, water supply lines are no match for you!

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