I have this assembly of stainless steel flex pipe and galvanized steel fittings at my cold water connection to my water heaters. The part where the cold water connects has a little bit of rust, and there were signs that the connection was leaking at one point, but the leaking has stopped. Naturally, I want to replace the rusty parts at a minimum to avoid complete failure down the line. A plumber told me that galvanized steel is contractor grade garbage and recommended replacing all the galvanized steel with brass fittings. However, my BS meter went off because I know that two different metals touching will cause galvanic corrosion. So what is the best solution here?

Pics of the install below. Not pictured is a shutoff valve on the cold water inlet. The shutoff valve has pex from the wall on one side and that stainless steel flex pipe on the other side which connects to the galvanized steel.

Maybe I answered my own question. I found some pics from a water heater installation manual. They have copper pipes from the wall connecting to brass compression fittings that then connect to the flexible stainless steel pipe. And they mention the flexible pipe could have a dielectric break inside.




But if the plumber wants to just make it all brass where the galvanized steel is, then there would be brass touching steel at the water heater cold connection right?

Yes but if you use a dielectric nipple or union, it prevents the reaction.
https://www.homedepot.com/p/Everbilt-3-4-in-Dielectric-Heat-Trap-Nipple-EBDN-HT-07/331674301

https://www.homedepot.com/pep/Everbilt-3-4-in-Galvanized-Steel-MIP-x-Sweat-Dielectric-Union-EBDU-07MS/331674288

When I spoke to the plumber that wants to do the work, he said an installation like the below wouldn't be a concern because the SS flex pipes have a rubber washer inside that creates a dielectric break. I was concerned with the brass and steel touching at the water heater too, but he said he's never seen that corrode, and he's done all brass similar to this for 20 years.

Most newer water heaters come out of the box with dielectric nipples installed. An easy way to spot this is if the nipple has a plastic liner inside. You could also call the manufacturers 1800 line with a serial # and they can tell you. Galvanized fittings are prone to rusting and are built cheap. I'd go brass off of the top if I were you.

Brass is the way to go


Galvanized will work but will rust over time


I have seen 75 year old galvanized still going strong and I have also seen it leak on threads and tees after 10-15 years as well.