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Question DetailsAsked on 4/13/2016

what is the brownish green gunk in my copper hot water line

I had a slight drip in a hot water line, so I shut off the hot water valve and removed the elbow that was dripping and a short piece of pipe inside the pipe was a build up of brownish green soft gunk. after putting it all back together and turning on the hot water all of the faucets in the house now have brown water comming out of the faucets.
What does this mean and how do I fix it?

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1 Answer


Here is a link to another recent similar question which might help - has several other links in it to other related questions about brown or black water.

The brown gunk would normally be mineral buildup (iron, lime, manganese most common) - either as a precipitated mineral or as a mineral-eating algae or bacteria (normally harmless to your body though can cause gastointestinal issues with some people if flushing through system in quantity) that eats the mineral and forms buildups. The green would almost certainly be corrosion products from the copper pipe deteriorating - though in rare cases (especially if pulling from surface water source or a tank) can be a plant algae coming in with the water and flourishing in the pipes, especially in non-chlorinated water.

If this was a significant buildup and hard - likely iron or manganese bacterial buildup. If soft, more likely sediment based or algae or lime based - especially if on well water or pulling from surface waters.

The brown coming from all the hot faucets was because when you drained the water for the repair a bunch of it got loosened up in the pipes (and maybe the water heater if you drained that down too) - 5-10 minutes full-flow flushing at ALL faucets (don't forget an empty dishwasher run with normal detergent and a clothes washer run with junk towels or grubby clothes or rags or such (not good to run it empty) to get the potentially stain-causing material out of its system AFTER you have flushed all other pipes to clean flow. Ditto to hot tub, sauna, jacuzzi, pool, etc - if you have a bypass drain at them use that to drain dirty water from the pipes feeding them - otherwise don't use any water in them until all other pipes are flushed out first so they don't get crudded up.

Check how clean water is by putting some water in a white bucket or large glass container or white bathtub to check for color and sedimentation - shows it better than just looking at the water flowing out of the faucet. In extreme cases can take 10-20 minutes full flow with shutting off and on to shake loose pieces into motion - best to run several at one time to the point where maximum amount of water is coming out, but not so many open that the pressure drops and flow starts dropping off. Typically one bathroom at a time - toilet, faucet, and shower/tub is a good full-flow condition.

Unfortunately, if you shake much of it loose it might clog the screens in the aerators on your faucets, so you might have to remove them to clean them. Especially on corroded or older faucets, this can sometimes mean replacing the aerator because you have to torque it so much it gets crushed or badly marred taking it off.

Don't forget to wipe down tub/shower and any synthetic or stone sinks/tubs/etc with tub and tile cleaner immediately after the flushing to prevent staining - especially of grout.

On the buildup/green/corrosion issue - plumber should be able to help identify source based on his experience in the area - might be an idea for you or him to cut into and check another pipe location or two to see if just one location or a general issue in the house, and if in hot or cold or both type pipes. He should be able to give you an idea of whether you are looking at imminent pinholing of pipes due to corrosion or if you just have normal copper corrosion that might last another decade or few. Be sure to look at condition of opened up pipes yourself because his tendency is likely going to be to promote total piping replacement for quite a few thousand $.

Generally - very generally with lots of exceptions - if the sediment is hard or a soft brown slush, sometimes that actually protects the pipe against erosion and corrosion. I have seen 100-200 year old pipes almost completely filled with it but zero corrosion of the metal piping. When the buildup is turning green (not just scattered green corrosion spots on the inside surface of the pipe itself) generally that means you have older pipes and a pretty substantial amount of electrolytic corrosion going on - normally occurs in copper pipes over about 30-50 years old, or 40-60 years old if brass/bronze pipes. But can be much faster in areas with acidic water or high corrosivity (high Langolier index) - so in some exposed or shallow non-sedimentary bedrock areas, areas with sulferous rocks (typically marine mud sediments or sulfur-producing areas), and some areas with minimal soil cover like high mountains and scoured-clean glaciated areas and such with very low mineral content in the water, which can actually make it corrosive because it tries to dissolve the materials it comes in contact with. That timeframe excludes locations within a foot or two of other metals like at dielectric unions or iron valves or appliances, where such corrosion builds up much faster - typically 10-20 years to bloom formation or leakage.

Generally, I recommend that if you see such buildup with distinct green tinge, or pretty substantial green corrosion on the inside of the pipe or more than scattered exterior green corrosion, that you start thinking pipe replacement once you get pinhole leakage like yours more than once a year or so. Of course, some people will tolerate more leaks than others, and of course where your piping runs makes a big difference too - you can tolerate leaks and repairs in a crawlspace or unfinished basement a lot more than in the walls or fully finished rooms or in the ceilings of rooms with full furnishings, memorabilia, and such. Can be a tough call just when to do the replacement, especially with older pipes - and some people like me take the approach that when a spot goes bad, don't replace just that spot if the piping shows significant corrosion - replace everything within reasonable reach at the same time, thereby eventually replacing all the plumbing area by area.

One other consideration - what was the cause of your leak. If at the solder joint likely a bad solder joint or over-fluxing. If eroded out in the bend (cavitation erosion) then that could be local or at many of your elbows. If general green spots of corrosion in the elbow and the pipe then that would be electrolytic corrosion, which tends to be systemwide unless that section is electrically ungrounded.

Answered 3 years ago by LCD

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