Water becomes corrosive if pre-treated with Chlorine or H2O2

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jrstevens

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Hello,

I've got a strange issue where my well water becomes corrosive if I treat it with either Chlorine or peroxide. I inject enough to get a residual (.5ppm-1ppm chlorine or 4ppm+ for peroxide). The residual is then removed via 2 cubic feet of catalytic carbon. The water ph is around 7.3 and doesn't change much pre vs post treatment.

My home is mostly PEX with the exception of the stub outs and the hot water heater hook up. Cold water is fine but I'm getting dissolved copper on the hot water side. I see around 500ppb on the first draw as well is visible discoloration of the water. If I bypass the chemical injection and cycle the water in the hot water heater, I get very little to no dissolved copper on the hot side.

1. Any idea why pre-treating the water with chlorine or peroxide increases corrosivity even after the residual is removed via catalytic carbon? Does chlorine/peroxide increase the amount of dissolved oxygen in water?

2. I may have to forgo chlorine/peroxide altogether. My AIO catalytic carbon system can remove the sulfur smell (6ppm), but the sulfur bacteria seem to re-establish itself in the house plumbing after some weeks. Would UV treatment be a viable option? Ex: the iSpring UVF55 12 GPM or similar.
 

water pro

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Hello,

I've got a strange issue where my well water becomes corrosive if I treat it with either Chlorine or peroxide. I inject enough to get a residual (.5ppm-1ppm chlorine or 4ppm+ for peroxide). The residual is then removed via 2 cubic feet of catalytic carbon. The water ph is around 7.3 and doesn't change much pre vs post treatment.

My home is mostly PEX with the exception of the stub outs and the hot water heater hook up. Cold water is fine but I'm getting dissolved copper on the hot water side. I see around 500ppb on the first draw as well is visible discoloration of the water. If I bypass the chemical injection and cycle the water in the hot water heater, I get very little to no dissolved copper on the hot side.

1. Any idea why pre-treating the water with chlorine or peroxide increases corrosivity even after the residual is removed via catalytic carbon? Does chlorine/peroxide increase the amount of dissolved oxygen in water?

2. I may have to forgo chlorine/peroxide altogether. My AIO catalytic carbon system can remove the sulfur smell (6ppm), but the sulfur bacteria seem to re-establish itself in the house plumbing after some weeks. Would UV treatment be a viable option? Ex: the iSpring UVF55 12 GPM or similar.
uv is for treating coliform bacteria, not IRB/SRB. your water is slightly alkaline so scaling is what you should be experiencing, not corrosion. does the raw water have sulfur smell on the hot and cold or just hot. what do the back of your toilets look like?
 

jrstevens

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uv is for treating coliform bacteria, not IRB/SRB. your water is slightly alkaline so scaling is what you should be experiencing, not corrosion. does the raw water have sulfur smell on the hot and cold or just hot. what do the back of your toilets look like?

Hello water pro,

When the sulfur smell returns in the house, the smell will be on both hot & cold. I can alleviate the smell on the hot side by turning the heater temp up to 140 degrees.

I forgot to mention another symptom when the water is pre-treated with chlorine or peroxide - the house water will develop a smell. Not a sulfur smell, something else. I'm guessing it is what some people call a metallic smell. If I had to describe it, I'd say it smells like "burnt water" if such a thing existed in reality.

I do not see any evidence of scale.
 

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Hello water pro,

When the sulfur smell returns in the house, the smell will be on both hot & cold. I can alleviate the smell on the hot side by turning the heater temp up to 140 degrees.

I forgot to mention another symptom when the water is pre-treated with chlorine or peroxide - the house water will develop a smell. Not a sulfur smell, something else. I'm guessing it is what some people call a metallic smell. If I had to describe it, I'd say it smells like "burnt water" if such a thing existed in reality.

I do not see any evidence of scale.
you mention you've used both H202 and Cl. If one wasn't completely cleared before the other is used, the combination will release an extremely high amount of oxygen. they are VERY reactive with one another.
 

jrstevens

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you mention you've used both H202 and Cl. If one wasn't completely cleared before the other is used, the combination will release an extremely high amount of oxygen. they are VERY reactive with one another.

Thanks. Through a combination of sample testing, flushing several hundred gallons of water, and time between the two, I don't believe there was any possibility of crossover.

Would you be able to please expand on UV being inappropriate for treating SRB? I can't find anything online. I actually only find that SRB is vulnerable to UV treatment.
 

water pro

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Thanks. Through a combination of sample testing, flushing several hundred gallons of water, and time between the two, I don't believe there was any possibility of crossover.

Would you be able to please expand on UV being inappropriate for treating SRB? I can't find anything online. I actually only find that SRB is vulnerable to UV treatment.
UV is used to treat gram negative bacteria (such as Shigella, Escherichia coli, Vibrio, Salmonella and coliform), viruses (such as Norwalk virus and rotaviruses), and protozoans (such as Entamoeba, Giardia, and Cryptosporidium. SRB, on the other hand, is anaerobic bacteria. It reduces elemental sulfur to produce hydrogen sulfide gas (rotten egg smell). SRB/IRB do not pose a danger to your health, while gram negative bacteria, viruses and protozoa do. H2O2 and chlorine can also kill harmful bacteria, viruses and protozoa, but they can also oxidize sulfur and iron. In this process the hydrogen sulfide gas is oxidized back to elemental sulfur, which than then be removed by mechanical means (such as filtration). Hydrogen sulfide gas can be corrosive to plumbing.
 

ditttohead

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We need a lot more information on your water to properly address your questions. Can you post a water test? TDS, calcium, magnesium, hardness, etc... all play a role in the LSI and corrosivity issues, not just pH. pH is a part of the equation, but many more factors need to be considered. Water above 7 can still be very corrosive. I would avoid anything from the manufacturer you mentioned above... H2o2 reverts to oxygen and is not usually recommended if you have bacterial issues since the levels of h2o2 required for a proper kill is a little excessive compared to chlorine.
 

jrstevens

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We need a lot more information on your water to properly address your questions. Can you post a water test? TDS, calcium, magnesium, hardness, etc... all play a role in the LSI and corrosivity issues, not just pH. pH is a part of the equation, but many more factors need to be considered. Water above 7 can still be very corrosive. I would avoid anything from the manufacturer you mentioned above... H2o2 reverts to oxygen and is not usually recommended if you have bacterial issues since the levels of h2o2 required for a proper kill is a little excessive compared to chlorine.

Hello dittohead,

Lab report attached. This is the raw water test before any treatment. Apologies for not attaching it in the beginning, but I thought it might confuse things.

The system order after the pump & pressure tank is -
1. 5 micron sediment filter
2. stenner econ fp injection system (currently bypassed)
3. 120 gallon retention tank (currently bypassed)
4. Fleck 2510SXT AIO with 2 cubic feet of catalytic carbon
5. Fleck 2510SXT with 1.5 cubic feet of softener resin and .5 cubic feet of tannin resin.

Regarding the peroxide, I only tried it as a test to see if the increased dissolved copper would still occur the same way it does with chlorine. I was otherwise okay with using chlorine and did so for several months.

I test the copper levels onsite with a Hanna Instruments HI747 low range copper colorimeter (range of 0 to 999 ppb). Without the chemical injection, I see very little to no copper in the house (treated) water. The copper present in the raw water report is filtered out by the time treated water enters the house. The copper I see on the colorimeter gets introduced via the hot water heater (again, only when pre-treating the raw water with chlorine).

Any ideas on what is happening?
 

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Reach4

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jrstevens

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MCLG for copper is 1300 ppb. https://www.wqa.org/Portals/0/Technical/Technical Fact Sheets/2015_Copper.pdf so not health threatening. They put copper into vitamin pills.

Is that discoloration green?

Could the copper be in the faucets, as well as the stubouts?

This effect of Cl or H2O2 is quite the mystery, IMO.

Thanks Reach4. I'm more concerned with leaks eventually forming on the copper pipes.

The discoloration could be considered green mixed with other colors. I suspect there is a high rate of deteriation of the anode rod, but I don't have a test kit for that metal.

The rush of discoloration happens when the water first starts feeling hot (2-4 seconds). I think hot water has less oxygen capacity than cold water, which led to my theory that chlorine or peroxide injection was increasing the dissolved oxygen which is then forced out of solution when the water heats up. I don't have a chemistry background though and was hoping someone might shed some light on the topic.
 

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ditttohead

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While many studies have been done trying to explain what is going on, the variances in water are limitless. I would start with the simplest fix, since it is more prevalent on your hot water, lets eliminate the sacrificial anode as a potential culprit. Search for a powered anode, these tend to fix a lot of obscure problems. AO Smith has been distributing them for a while now but there are many brands on the market.
 

water pro

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Hello dittohead,

Lab report attached. This is the raw water test before any treatment. Apologies for not attaching it in the beginning, but I thought it might confuse things.

The system order after the pump & pressure tank is -
1. 5 micron sediment filter
2. stenner econ fp injection system (currently bypassed)
3. 120 gallon retention tank (currently bypassed)
4. Fleck 2510SXT AIO with 2 cubic feet of catalytic carbon
5. Fleck 2510SXT with 1.5 cubic feet of softener resin and .5 cubic feet of tannin resin.

Regarding the peroxide, I only tried it as a test to see if the increased dissolved copper would still occur the same way it does with chlorine. I was otherwise okay with using chlorine and did so for several months.

I test the copper levels onsite with a Hanna Instruments HI747 low range copper colorimeter (range of 0 to 999 ppb). Without the chemical injection, I see very little to no copper in the house (treated) water. The copper present in the raw water report is filtered out by the time treated water enters the house. The copper I see on the colorimeter gets introduced via the hot water heater (again, only when pre-treating the raw water with chlorine).

Any ideas on what is happening?
the addition of an AIO system combined with Cl injection following retention is redundant. you only need a GAC backwashing filter to remove residual Cl (2ppm) after retention. The retention tank will settle any oxidized iron or sulfur (which can then be blown down periodically). I would also suggest replacing the 5 mic cartridge filter with a 20 mic.
 
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