Making soft water less corrosive

[Anonymous]

My plumbing is corroding — I am getting metallic sediment from my hot water only. I have a water softener.

Well water — Hardess as CaC03 376 mg/litre (around 22 grains), alkalinity as CaCO3 319 mg/litre, conductivity 915 us/cm (high), ph 6.96. The Langelier Index of the hard water is -0.37 (slightly corrosive).

Soft water (into my hot water tank) — hardness is zero, ph is 7.25, alkalinity 277. Note that the soft and hard water tests were taken 6 months apart, so things may have shifted a bit. I have been told that the soft water is highly corrsive (according to Langelier Index).

How can I make the soft water less aggressive, or how can I protect my plumbing? I am thinking about installing a Polyphosphate feeder. Will this work, and any suggestions on products? Or, is there some other chemical treatment I can use? Should I give up and put hard water into the hot side, or mix soft and hard water?

[daveroconnParticipant]

I thought your question required some discussion in another forum at waternet.com my field of expertise in in reverse osmosis.

Responses:

RE: Taken from Masterplumbers .com: Chuck Fitzgerald: 8/18/00 11:38:31 PM
Check out if the sediment is magnetic, if so the hot water heater tank is acting as a sacrafical anode, and or the installed anode is not fuctioning, there may be either improper electrical grounding, galvonic corrosion, or stray voltage (DC or AC). If not magnetic, are they plastic (acrylic) or glass (cermaic) like, the interior tank coating may be degrading, check the specs on the coating. Gas or electric?, the heating coil could be degrading. Bacterial action and or certain chemical precipitants (sulfides, carbonates are dark colored) may be forming in the tank. Sulfer reducing bacteria (ODOR?) will give dark deposits, slimes.
Polyphosphate use in either of the above circumstances will either not help or only make the problem worse. With the hardness you have the tank will quickly form carbonates and clog up.
In regards to other treatment options, see gary’s comment in the sodium question, I TOTALY agree.

RE: Taken from Masterplumbers .com: Al Reo: 8/19/00 3:04:32 AM
There has been a problem lately with the plastic dip tubes in many brands of water heaters breaking down into pieces.
I read about this in a plumbing trade magazine, but the website is down right now. If I can find it tomorrow I will pass that info along.

RE: Taken from Masterplumbers .com: Chuck Fitzgerald: 8/19/00 9:09:21 AM
The tubes are a white plastic, if the deposits are white or off white in color you got it.

RE: Taken from Masterplumbers .com: Gary Schreiber, CWS V: 8/19/00 11:07:05 AM
How many times do we have to say this:
Softened water does not increase water corrosivity. I guess a million times is not enough.
The Langlier index REQUIRES hardness in the calculation otherwise the calculation is USELESS. Calculate the corrosivity of the unsoftened water. That predicts what the calcium carbonate stability of the water is.

Plumbing protection can be done when you find out what the corrosion cause is. Phosphate may or may not be the answer. The question states a “metallic sediment”. What is it? Answer that question and you will start to find the answer.

As you see there are some differences in opinions use the answers that make sense to you but don’t be affraid to ask for help.

[jbosloyParticipant]

I had the hot water sediment analyzed by a lab. It is definitely metallic, made up of things like magnesium (from the hot water tank anodes), copper, aluminum, zinc, manganese, iron, nickel, etc. (details below). I have copper tubing, with some brass fittings.

I was told by the lab that the Langelier Index of the raw well water is -0.37, which is slightly corrosive, but pretty balanced I think. The same lab told me that the soft water was very corrosive according to the Langelier Index, but Gary points out that that analysis is invalid.

Since the Langelier index of the well water is fairly balanced, but my water is very hard, do I still need a water softener to avoid calcium build-up?

Sediment analysis details. All figures are micro-grams per gram of the sample:

Magnesium (Mg) 172,000
Copper (Cu) 87,000
Aluminum (Al) 38,000
Zinc (Zn) 26,600
Manganese (Mn) 6230
Iron (Fe) 2,250
Nickel (Ni) 1,400
Cobalt (Co) 130
Lead (Pb) 90
Barium (Ba) 80
Silver (Ag) 10

All other checked elements were below the measurable limit.

I assume that the elements like lead, barium, silver, cobalt are impurities from whatever is corroding.

What would have aluminum, zinc and nickel, and manganese, which is the majority of the sediment (other than magnsesium)?

My well water did not have any measurable amount of manganese, but it does have some iron.

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