I just moved into my house with brand new PEX (uponor) plumbing. I used clear for the hot and cold instead of red and blue, because I bought everything myself and I thought it would prevent wasting too much. I installed the PEX tubing myself after buying a new Milwaukee tool. This was my first PEX DIY project, but I have a fair bit of experience with lots of remodeling trades.

Anyway, we have been using the plumbing for about 6 weeks. I just noticed that the hot water tubing right near the water heater (commonly abbreviated as HWH) now has a green hue for about 12-24" past the heater. The water itself is not stinky or green - although I do notice a slightly different smell than with my old copper plumbing. There is about 3 feet of SS flex and copper between the water heater and the PEX. Our County inspector approved everything. The water heater is electric and it is about 5 years old, purchased from someone on craigslist. The water heater was empty when I moved it into the house, but I didn't try to clean it with anything.

So, what is causing the PEX tubing to turn green? Should I make the water heater hotter? I don't think it is above 120F, but I haven't measured it. Should I figure out how to inject bleach into the system every once in a while?

Edit: added picture. It turned out better than I expected.

pipes coming from water heater are on the left


8 Answers 8


I am a professional plumber and I have been using PEX tubing for 20 years and I am also manufacturer-certified to do so.

The only time I've ever seen this green color in PEX tubing it was algae. The pipe was a cold water supply line that was wrapped with heat tape and pipe insulation, and run above ground underneath my camper. When I removed the pipe it had algae growth along its whole length.

However, the algae will not stick to the pipe. When you kill it, it will just wash away out through your faucets; just make sure you remove your aerators in order not to clog them.

  1. Shut off the water supply line to your water heater.
  2. Drain some water out of your water heater from the drain valve.
  3. Disconnect the supply line from your water heater, so you can pour your bleach in from there.
  4. Reconnect your water heater and run hot water out all your faucets until you can smell the bleach.
  5. After letting it sit for a sufficient amount of time, flush all the water out of your hot water pipes and water heater until no more bleach is detected.

This will kill your algae, but you may still have it inside your pipes. You might need to tap on the pipe to knock it loose before flushing.

In my case I drained the pipe and the algae dried up and fell from the pipe. Or you could remove and replace the affected area.

  • Turn the water heater off before draining water from it, or you will be replacing the elements.
    – TomG
    Commented Jun 4, 2013 at 1:16

Translucent containers that hold water tend to grow algae. This is because of the constant moisture and the light getting through...an ideal environment for algae to grow. Since there's nothing you can do about the moisture, I recommend using a non-translucent tubing (such as the red or blue) for your water lines.

  • 2
    Maybe the algae still grows in the red/blue lines, but you just can't see it? :) Bummer, though. I guess I could replace it and wrap it with insulation and then wait 6 weeks to see if new algae grows.
    – brfox
    Commented Jul 25, 2011 at 3:57
  • 1
    If you think its algae try an experiment: Cover half of the clear PEX that is turning green with something that blocks light. Tape, cardboard, whatever. Wait a few days (weeks?). If its algae the covered part of the pipe will not be green, but the uncovered part will still be green.
    – Freiheit
    Commented Jul 28, 2011 at 16:04
  • 1
    @brfox Yep it's translucent, the stuff grows, you just can't see it. PEX should be in a light-free environment. Commented Jan 2, 2013 at 7:07

Probably algae growth, as Shane says, however there's a much easier fix than replacing it: insulate it. (which is something that you probably should've done anyways!)

  • I insulated most of it, but not the laundry room yet since we are still finishing up some stuff.
    – brfox
    Commented Jul 25, 2011 at 3:56
  • @brfox Is the green stuff location at or near the exposed pipe... or is it impossible that it's algae?
    – Michael
    Commented Jul 25, 2011 at 4:03
  • Yes, its is exposed to the light. But only indirect light from the hallway - never direct sunlight. And it is just the section of pipe closest to the HWH heater, so it must be a temperature thing as well. The cold water line has the same amount of light, but is not green at all.
    – brfox
    Commented Jul 25, 2011 at 4:20
  • Hmm. My problem with the idea that it's algae is that there appears to be no algae in any of the other pipes. Copper sulfate is a common pool chemical used to get rid of algae, although I have no idea if plain old copper would kill the algae and thus rule out the algae theory. It does appear to be coming from your water heater, though, and there shouldn't be any algae in there anyways... there's no light. Algae doesn't need all that much light, but I'd guess that it needs a lot more than what the inside of your water heater is getting. Starting to think that the green stuff is instead...
    – Michael
    Commented Jul 25, 2011 at 5:07
  • oxidized copper ( google.com/… ) ... but on the other hand, the color appears to match algae more than it does oxidized copper, which typically has more blue in it.
    – Michael
    Commented Jul 25, 2011 at 5:14

Maybe this will help: http://www.mass.gov/dep/water/drinking/color.htm

Green Water

In cooler climates, the most common cause of green water is copper plumbing corrosion. If this is happening, the water will usually have a bluish-green tint and/or will leave a bluish-green stain on porcelain if the water drips from a faucet. Copper corrosion can also be caused by your electrical system being grounded to your water pipes, especially if you have a mixture of pipe material (e.g., some copper and some galvanized steel.). Green water may also be present in homes with copper plumbing that is less than two years old. The presence of copper can be confirmed through analysis. The EPA has a copper fact sheet.

Green water can also be caused by dezincification of poor-quality bronze alloys found in valves, water pumps, and water pump parts. This problem can occur in high-rise buildings and large industrial properties where the water is pumped to storage tanks. The water may also be tested for zinc.

During warm weather, green water may be caused by green algae in water supplies served by reservoirs or rivers. Algae are single-celled plants that readily grow in bodies of fresh water. Algae are not a health threat and reservoirs can be managed and monitored to prevent algae from growing to the point were they discolor the water. The water supplier through filtration may also remove algae.

  • The water is not green, just the PEX tubes. There is hardly any copper in the house.
    – brfox
    Commented Jul 26, 2011 at 4:52

Are you on well water? Have you had the pH of you water tested – whether you are on well or city water? Lower pH water is corrosive to copper pipes. Seeing that you have part copper piping in your installation, the green you are seeing may be leaching from the copper pipes. Hot water also allows the leaching to occur even more than cooler water. This may explain why you are seeing it in the hot water tubing and not the other.

Also, use caution in pouring chlorine bleach into your PEX pipes. This may weaken the pipes, same as exposure to sunlight. Do your research before using bleach!


It actually has to do with your brass fitting, these fittings are corrosive when attached to copper.

  • brass is allowed to be used as a transition between copper and a dissimilar metal, it's not corrosive.
    – xhainingx
    Commented Apr 4, 2018 at 20:37

I'm a plumber and have encountered this on a few occasions. I believe it is a combination of opportunities for algae to grow in your pipes. Check the reservoir; it starts there and adds all the elements for the algae to thrive then be transported to you where, in areas it collects light and warmth to add to its growth.

Cover any pipes that are transparent to any degree of light. Without light you limit its ability to continue growing. Introduce a fine micron strainer that can be rinsed and reused, before it gets to the pressure regulator for the geyser. This has worked for me.


This happened because of build up in the hot water heater and hard water in the area. Remember if they re-pipe your home and never replaced the heater, the old junk from the old pipes is still setting on the bottom of the water heater.

"replace heater if it's over 6 years old or do nice flush if it's under 6 years"

  • Who is quoted here?
    – isherwood
    Commented Apr 3 at 15:16

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