Toilet Water Supply Line Through Floor: How To Install (DIY)

When building a toilet in new construction, water supply lines generally run through the walls. But if you want to add a new toilet to your upper floor, perhaps you’re wondering whether you can prevent breaking the wall and run the toilet water supply line through the floor. Luckily for you, that’s possible. 

To run your toilet water supply lines through the floor, measure the distance from the toilet center line to where the water pipe would come out. Respecting the toilet rough-in distances is crucial for a proper filling of the tank. The type of pipe you install can make a difference in terms of durability. Copper pipes are your best choice.

Can You Have A Toilet Supply Come Straight Up Through The Floor?

Yes, an ordinary toilet can have a supply line coming straight up through the floor. This type of installation actually comes in handy if you want to add a new bathroom to your existing home. By running the pipes through the floor to the location of your toilet, you can avoid breaking the walls and can only bore one hole into a ceiling/floor. 

In most cases, people run a toilet water supply line through the floor when building a new bathroom right above a bathroom or laundry room. However, you can run the line through the floor from the basement if you feel it’s easier than accessing it through the wall. With this in mind, let’s see how to install a toilet supply line.

How To Install A Toilet Water Supply Pipe Through The Floor  

Whether through the floor or a wall, toilet water supply lines are fairly easy to install. Follow the quick steps below for a DIY installation.

What You’ll Need

  • Water supply lines (preferably copper pipes, but PVC could also work)
  • Drill 
  • Drill bits
  • Hole saw 
  • Reciprocating saw
  • Level
  • Tape measure 
  • Pipe fittings 
  • Clamps 

1. Determine the pipe location

The first thing to do when installing a new toilet water supply line is to determine its location. The pipe should be located about 8 inches from the toilet center line and end about 8 inches above the finished floor.

For this reason, it is easier to take all measurements after you’ve tiled the bathroom. Otherwise, you can estimate the floor’s height by measuring the tile thickness and accounting for about an extra quarter of an inch of tile adhesive. 

The toilet center line corresponds to the center of the flange. Measure 8 inches from this point to the left of the toilet and mark it on the floor. 

Now, measure 8 inches from the floor up the wall and place a mark. You can bore a hole for the water supply line at any distance between the wall and the 8-inch mark from the toilet center line. Keep in mind, however, that the closer the line is to the wall, the easier it will be to secure it.

2. Bore the hole

Set your drill up with a ¾-inch spike bit. A wood bit is generally enough if you’re only boring through the subfloor, but you may need a masonry bit if you also have to drill through the tile. Drill the hole through the base plate to the ground floor or basement. 

3. Cut the line 

Measure the distance from the water supply line to which you plan to hook the toilet line, then cut an appropriate length of the new pipe

Most plumbers use copper supply lines since they are durable and look better than PVC lines coming out of the floor. However, you can use a PVC pipe as well. 

Using a pipe cutter at this stage is the best choice if you want to obtain a clean cut. Alternatively, cut the pipe with a saw and smoothen its edges with sandpaper.

4. Install the pipe

Start with the top of the pipe what will then connect to the toilet tank and install a push-and-click fitting. 

Insert the pipe into the hole and fasten the elbow with screws to the wall, in correspondence to the 8-inch mark you measured earlier. You can now decide whether you want to install a pipe extending from the floor supply line toward the center of the toilet or use a flexible water supply hose to connect the supply line to the tank.

If you decide to install a pipe extension, measure about 2 ½ inches of copper pipe and push it into the empty slot of the elbow fitting. 

5. Connect the toilet supply line to the main water supply 

With the new line in place in your new bathroom, it’s time to connect it to the main water line. This doesn’t have to be your house’s main supply line, but the water line from which you plan to draw water.

If the supply line is already in use, you’ll have to drain it before proceeding. To do this, turn off the main water shut-off valve and open the highest faucet in your house. Then, open the lowest faucet in your house, which could be on the ground floor or in the basement, and wait until the water stop flowing. 

Mark the point where you want to hook the toilet line to the existing water pipe and cut out a section of the pipe so that you can fit a tee.

Install the tee fitting with the empty slot up, then push the new toilet supply line into the fitting. Depending on the fitting type, you may have to seal the connection with a plumber’s tape or glue. 

You can now hook the new supply line to the toilet if the toilet is already installed, or plug it in and turn on the water. Wait for the pipes to fill and check for leaks. If you have connected the toilet line to the tank, check if the tank fills correctly.

Final Thoughts 

Installing a toilet water supply line through the floor is an excellent DIY project for those who want to save some money. We hope this guide can help you fulfill the project successfully but don’t forget: if you’re in doubt, don’t hesitate to hire a plumber.

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