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How does a plumber whether water pipes are rusting from electrolysis or the hot water heater is deteriorating?

Very rusty water appears in my bathtub within 5 seconds of turning on the hot water faucet and then within a few seconds clear water flows. Rust doesn't show up anywhere else in the condo water system including the separate shower which is located 1 foot away from the bathtub. 2 units in my 10 year old condo high rise have had water leaks in the copper water lines (hot water side) that run overhead in the ceiling hallway of the unit. It was found in both cases that electrolysis was the culprit. Several wire hangers were of dissimilar metals to the copper lines. In my case how does a plumber go about determining whether the rust is hot water heater related or if electrolysis is the issue.

Donna Conly
homeowner - Denver, Colorado, USA
November 3, 2011

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If your plumbing is all copper, then the only source of rust is the steel water heater. Your piping should all be either copper or plastic. Iron pipe in domestic water lines is a no-no. Ten years seems a bit short life for a water heater, but it could be rusting away. if so, it will soon leak.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
November 7, 2011

My question is: what procedures would a plumber use to determine whether my hot water heater is rusting or whether the original installation of water lines involved some mixture of metals. Rust only shows up at the tub w/in 2-5 seconds of running hot water. No rust shows up at the shower although the shower is 1 foot from the tub. No rust shows up in the Washing machine although the washing machine is in the room opposite to the bathtub and the plumbing runs in the walls between the bath and w/d room. What is the best way to determine the source of the rust?

Donna Conly
- Denver, Colorado, USA
November 9, 2011