Today a contractor installed a water line from the main to my house. During the tie in, the pipe continued to leak. The fitting thread was found to be defective, so the contractor placed 3/4 line about 16 inches from the main to the 1 inch line, and then fed the 1 inch to the house and water meter.

Will this 3/4 to 1 inch affect my flow or pressure? Is this ok to do? I am not 100% sure this was right.

  • I'm not going to claim enough expertise on this to answer definitively. But--a short section of 3/4" pipe shouldn't be an issue when a 3/4" supply is fairly standard for a house anyway, and your water supply lines branching out inside the house are all 1/2" and 3/8". No water outlet is bigger than 3/8". Also, if you have 1" on both sides of a short 3/4" section and push a certain volume of water, the water is just going to move faster through that 3/4" section, and at lower pressure (Bernouli's principle), then move slower and at higher pressure again in the 1" section on the other side. – Craig Aug 12 '15 at 22:42
  • I think you're fine, but if somebody has deeper insight into this I'll happily leave it to them to share what they know. – Craig Aug 12 '15 at 22:42
  • Thanks Craig Just to clarify the 3/4 is tapped into the large main water pipe out in the street A small section 16-20 inches it then connects to a 1 inch line goes approx 50 feet into house and meter – user41412 Aug 12 '15 at 23:16
  • The meter then reduces to 3/4 for the house – user41412 Aug 12 '15 at 23:21

You're right to be suspicious. I'm not sure about code, but to me this just looks unprofessional. Narrower pipe does result in pressure and flow loss. Expansion also has the potential to create eddy currents which could accelerate erosion of fittings on the output side of the final 1" fitting... that said, contraction/expansion happens normally at most fittings anyway. The good news is, this is such a short section of pipe, that even if you absolutely require a 1" main the effect is entirely negligible. Since you effectively have a 3/4" main inside the house, doubly so.

  • It would be nice if someone had an equation considering 1/16" of a 1/16" diameter would render it useless. Edit...I think its this "pressure loss" equation. Anyone understand it? – crokusek Apr 3 '20 at 22:21

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