I have 3/4" copper supply from the street, running (alas) through a concrete slab. The supply emerges in the bottom of a closet. It was originally plumbed, just where it emerges, with a reducer fitting from 3/4" to 1/2", before the whole house shut-off valve. Next in the vertical run is a short bit of 1/2" pipe, and an elbow. Then in the horizontal run, a longer bit of pipe into another elbow, which is inside the back wall of the closet. The piping next goes up vertically inside the wall to the ceiling, where (presumably), the flow is split to the water heater and the cold supply.

I have (naturally) a pinhole leak just after the shutoff, which is also not closing off completely. The proposal, from a plumber, is to:
- Remove everything, starting from the original reducer on up to the second copper 1/2" elbow, inside the wall.
- Replace, starting where the 3/4" supply enters, with a 3/4" shut-off valve.
- Continue to the wall with a 3/4" elbow, 3/4" pipe, then a reducer to 1/2" at the elbow inside the closet wall.

The water pressure is usually very good - I don't have the actual psi number, but this is a public water system.

Is there any particular reason that someone would propose 3/4" all the way back to the wall, before reducing to 1/2"? Is this a code, or a pressure issue? (We generally do DIY, but this is a rental that we need to get back into service, so we'll probably hire a professional this time.)

Many thanks!

if the old shutoff is not working it needs to be replaced. it is not that much more work to replace a few fittings and some pipe as well.

The reason someone would propose to install 3/4" is because 1/2" pipe is a pitiful supply for anything other than a couple of faucets, and definitely NOT for an entire home. More than likely the reason you have the pinhole(s) is because the velocity in 1/2" tubing is so high that it erodes the inside of the pipe, especially at tees and elbows.



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hj - That's food for thought. Perhaps our long-range plan to convert to PEX should be moved up on the list. We've got a slight problem with acidity in the water, and no place to easily put a treatment system. Thanks.



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Cu tube needs 2 conditions to last:

1 - proper flow velocity = 6 feet per second or less, 3-4 recommended

2 - sliiiiightly alkaline water

+ recommended, but not required

3 - quality ASTM rated "L" tube

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

quote; 3 - quality ASTM rated "L" tube

WE have been using type "M" copper since the 60s in residential buildings.

then the flow velocity (proper sizing) becomes MORE important as there is a 'thinner' wall

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

I did a bit of research on pinhole leaks in copper.
I know Montgomery county, MD has had a big problem with it.
From what I recall, water velocity in the pipe has nothing to do with it.

I believe the final determination on pinhole copper leaks is the PH of the water.
The closer to pH-7 (neutral) the better. What was happening as I recall, is as
the pH changed up or down, any solids in the water would tend to settle and latch onto the pipe wall. Hence horizontal runs always had more problem then vertical. Once the solids latched on the pipe wall, they would start an oxidation process (for lack of a better term) and then eat the pipe from the inside out. Naturally with "L" instead of "M", since the pipe wall is thicker, it would take longer to eat through the wall, but that does NOT stop the problem from occurring.
Only changing the pH seems to have resolved the underlying problem. I believe most water companies now understand this and do a good job to try and control the pH, If your on well water that is another issue.

My2Cents