Q&A / 

Properly Size Your Water Lines

My guess is that most people don't think twice about the water that will flow from the faucets in their new homes. You may not even give a second thought to the noise water makes when rushing through water lines. Because you are moving into a new home, my guess is you might assume a waterfall of water will cascade from each faucet and hose bib. Don't count on it. Your builder or plumber may have made a few mistakes that can restrict the amount of water that flows from faucets. These same mistakes can also cause significant water pipe noise that drowns out conversation and other pleasant sounds around your home.

If you are in the planning stages of building, you can correct these problems before they happen. A water supply pipe of a given size can only supply a given quantity of water at a given pressure and a given hydrostatic head. Hydrostatic head commonly refers to the vertical distance a water line extends. If you are trying to push water up a pipe from a basement to a second floor, gravity is doing its best to exert an opposite force against the water pressure. Gravity becomes your friend and increases water pressure if you store your water up on your roof, but how many people do you know have 5,000 gallon storage tanks in their attics?

Plumbers and builders know that people rarely turn on more than three or four plumbing faucets at the same time. But it can happen. If you want a plentiful supply of water to flow from each faucet, you must be certain that the main water line entering the house and the main feed line within the house is three-quarter inch in diameter or possibly one inch in diameter. This larger sized pipe can carry a significant amount of water.

All too often, a rookie plumber might start to prematurely reduce the size of the water lines in a home. If you see one-half inch diameter water lines that serve two or more fixtures, trouble may be just around the corner. If your new home has three or more bathrooms, consider keeping the cold water pipe size one inch until it has served the water heater, the first bathroom group and possibly one or two outdoor hose bibs. The main water line can then be reduced to three-quarter inch diameter to serve the remaining bathrooms, laundry room, hose bibs, etc. One-half inch diameter pipes can branch off the three-quarter inch line to serve individual fixtures. Extend the three-quarter inch line until you get to the final two or three fixtures in the house.

Pipe noise is also a function of pipe size. Larger diameter pipes create less noise because the velocity of the water moving through the pipe towards the fixture is lower. You can also minimize pipe noise by specifying a thicker pipe size. If you are using copper tubing in your new home, it is very likely that type M copper will be used indoors. This is the thinnest pipe allowed by most plumbing codes. Thin pipes transmit noise more readily than thicker-walled pipes.

The next thicker pipe type is L copper. Look at a piece of L vs. M copper and you will not see any difference. But pick up a 10-foot long piece of each and you will immediately realize the type L copper weighs more. This extra copper absorbs sound. The fantastic news is that the cost upgrade for type L copper in a typical residential home is less than $75.00. This is a one-time fee that allows you to have quiet water supply piping for the life of the home. It is a very small price to pay for peace and quiet.

Finally, be sure the pipes are not in a bind as they pass through wall studs, wall plates and floor joists. The holes need to be slightly oversized so the water pipes can expand and contract freely. Pieces of rubber that absorb vibration can also be installed between the pipes and any wood framing. Installing the strips of rubber can be a hassle, but any acoustical engineer will tell you it helps to stop noise transmission.


16 Responses to Properly Size Your Water Lines

  1. I have a new house and my water comes from a well. The builder
    had young plumber to do the plumbing but he plumb my riannis
    wrong so I just got done replacing the pipe. My question is
    the pipe from the well is two inch then he put a three inch piece of
    one inch to a shutof then ran three quater to half thru the house.
    I am in the process of fixing it. I would like to know if I should replace
    the pipe with one inch to half inch to my fixtures. Thank you

  2. I'm replacing a water line supplying a three bedroom two full bath home. Distance from meter box to house is 400 feet, water diameter line do I need? PVC vs PEC?

    • You won't go wrong with an 1.5-inch diameter line. What plastic is approved by your water company?????? Do your research online for FAILED stories about either material in your area.

  3. I just read your article and appreciate the information. Above our water meter on the house side is a pressure gauge that reads about 55-60 psi. When more than one tap is opened, the psi drops to about 20. The main is 3/4 inch and connects to the meter which is 5/8ths. Do you have any suggestions on how to maintain a 50-60 psi with more than one tap open? Thanks.

  4. We had water coming in to the house gushing in becaseu the metal piping separated from the water line fcoming into the house, so the shut off valve would do no good!!!! The plumber came out and recommended we replace the water oline coming in, because due to settling, the line is pulling out most likely causing what happened last night. Is this accurate>

  5. I'm building NEW house requiring 400+' run going UP about 100 feet. We going from a well with pump capacity of 20 GPM and currently running at 78 psi.
    Our pump is constant pressure 3 phase type (love it!!!).
    I expect to install an in-line pressure pump up there although I got good flow in test up there with a hose.
    What would you recommend for line running from the well up to the house? I was planning on PEX but probably need to run it inside larger PVC to protect it in this crushed sharp shale environment.

  6. I need to find a way to size the water service for buildings from the city main to the meter in Hoboken N J city pressure is 90 psi

  7. After 2 polybutelene leaks in the same week, I am re-piping my house with PEX in NW FL. I have a 3/4" main supply line from the street to the 2100 square foot, 3 bath, house with irrigation sprinklers and pool. Pressure at one of the external faucets is 55 psi. House to street is approximately 100'. Distribution of the supply via manifold to the farthest faucet in the house won't be much more than 100'.

    Is there any harm if I increase the size of the supply line entering the house from 3/4" to 1", allowing for the potential to re-pipe the supply line from the structure to the street if I ever feel that the water flow is no longer adequate?

    In other words, I'll have 1" diameter pipe at the street, reduced to 3/4" pipe from the street to the house, then expanded back to 1" before entering the house. I figured since I have to open the walls to route the new PEX, I might as well maximize the pipe size now with the walls open, thinking that in the future, if I do have flow problems or install additional plumbing fixtures, all I would have to do at that point is re-pipe from the house to the street. Is there an issue with the reduction and subsequent expansion, with no definite plans to eliminate the reduction in the future?

  8. We are running water line from meter to new house - about 4000 feet. What size and psi line would you recommend? Thank you.

  9. I have 1\2 inch PVC water lines in my house and a 1\2 feed line coming from the water main.Will my water pressure increase if I increase the outside feed pipe to 1 inch?

  10. How can I determine the size of the branch line of my piping if I have main pipe size of 4 inch. I am planning to have 3 branches, these three will flow going to the main and this these should not be overflow when they are simultaneously open at full flow. Please help. thanks

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