I have a strange water line arrangement coming into the house and I would like to know what line is for what - I understand that I have cold 3/4 pipe coming in to the house and cold 3/4 pipe going to other parts of the house and the hot water heater. The hot water heater has 3/4 line going to the rest of the house.

Now here is my question where on earth do the 1/2 inch lines go (or where should I expect them to go?)

The Red rectangle in the picture is the concrete floor. The lines are all copper pipe.

Water hookup

  • It sounds like you’re describing Pex plumbing. The location where the water is distributed is called a manifold. Why do you call the arrangement in your house strange?
    – Tyson
    Commented Jan 22, 2018 at 11:06
  • The arrangement is not a manifold, and I do not have PEX - I have copper lines. The lines at the red area are the concrete FLOOR.
    – Ken
    Commented Jan 22, 2018 at 11:08
  • 1
    Thanks. That’s a great addition. You might also post an actual photo.
    – Tyson
    Commented Jan 22, 2018 at 11:10

2 Answers 2


Usually, the 1/2" lines go to a single outlet such as a sink, tub or laundry and the 3/4" line or lines run to multiple devices. For example, the 3/4" line can feed many devices with 3/4"X1/2" tees supplying each faucet with a 1/2" supply line. This way you will usually get maximum flow at your faucet even if someone else in the home is using water at the same time.

  • the laundry is connected to the 3/4 lines via a tee reducer just above the points you see in the diagram so I know they aren't that . These go into the concrete, just like the 3/4 - I understand the 3/4 splits off to 1/2 at my faucets/toilets/showers and external faucets. These two are hot and cold which leaves me baffled and does not make any sense. They are sweated to the pipes and I don't want to cut them and push die in them to try and find out.but sure would like to know as I am at a loss.
    – Ken
    Commented Jan 22, 2018 at 11:54
  • If the smaller lines have valves on them you could shut off that line and see what sink etc that shuts off, The 1/2" lines could feed a single device that is located by itself, say a powder room or a bathroom set away from the other rooms, and therefore did not need a 3/4" supply line that would feed multiple items.
    – d.george
    Commented Jan 22, 2018 at 12:53
  • if they had valves I would have tried that - but I guess you had to say it some people don't think that far. I have 2 Bathrooms right next to each other, a Kitchen next to the laundry and 2 outdoor faucets. The laundry is connected right above those pipes. The two outdoor faucets only have cold water (so why the hot is the same.) I am wondering if someone has hidden a set of faucets like maybe the laundry was relocated but I do not see anything anywhere.
    – Ken
    Commented Jan 23, 2018 at 19:52

Years late but you have 2 separate 3/4" incoming supply lines split to 1/2" it's to keep pressure to different fixtures consistent

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