Funnily enough, this is technically true, but would only manifest in a warped reality.
In the acidic/caustic scale, regular water is just slightly on the caustic side of neutral. (pH 5.5 or thereabouts?) - It won't strip the pipes it runs in. But that's not the kind of water we're talking about here. That would be pure distilled water.
It's the near-universal cleaning agent. Because of the complete lack of impurities, distilled water has the ability to absorb fair amounts of almost anything it gets in contact with. It also tastes really bad. (The taste of "nothing" for regular water is our calibrated baseline with various minerals and other impurities. If you take all of that out, the perceptual difference between expected and experienced is quite stark.)
For what it's worth, cavitation and turbulence are much more likely culprits to eat the plumbing material. Also: shoddy quality will always cause problems, regardless of your choice of materials.
Only acidic water (and strongly so) will damage copper pipe.
Most copper pipe will easily last 50-100 years, if not more.
Flouride isn't added in any sort of concentration that would measurably change water Ph.
And more.
Your saturation index is what drives water’s interaction with the surfaces it touches, not just pH. If the index is too high it will deposit what it’s carrying (scale) and if it is too low it will pick up material from the pipe it’s flowing through (corrosive).
These are used in swimming pools, but originally the saturation index was developed by Langelier to protect city pipes from corrosion: https://en.m.wikipedia.org/wiki/Hard_water#Langelier_saturat...
IIRC most cities try to run a high saturation index to intentionally lay down scale that further protects the pipes from corrosion.
It may be true that fluoride isn’t in sufficient quantity to impact the saturation index, but that is distinct from pH.
2) There is theory, and there is practice in the field. What you’re referring to is the equivalent of ‘wet bulb temperature’ for temps. Which is a thing, but water conditions for a given area rarely vary like temperature will - and are in control of the local water treatment plant. What you’re referring to was specifically made to measure and help control these conditions.
If copper piping is allowed by local code, they’ll know - and keep it within these ranges. Areas with water that is not easy to keep within these ranges will also corrode galvanized pipe (commonly used for water in most areas), and will likely also corrode brass fittings and valves (including back flow valves) commonly used in many areas, leaching lead, copper, etc. among other things. Those areas prohibit them by code for that reason.
Copper piping will generally not corrode unless PH is < 6.5 or > 8.5, which is significantly outside what most would consider reasonable water quality.
I personally have a well in an off grid location with 6.2 PH, and use only CPVC for that reason. Where I live, I’ve done some retrofits and replaced 75 year old copper pipe that was good as new inside.
I think I’m misunderstanding you. Your original comment was “that’s bullshit” but this seems like it’s in rough agreement.
IIUC copper pipe will last for 50-100 years IFF you pass impure water through it. Pure water will eat the pipe. Same with galvanized steel and brass like you pointed out. So the city treated it with _something_ to keep the water from eating pipe (knowing copper pipe is code) and I’ve anecdotally heard that part of that “something” is fluoride.
pH = 7 (pure water)
TDS = 0 mg/L
Calcium = 0 mg/L (or ppm) as CaCO3
Alkalinity = 0 mg/L (or ppm) as CaCO3
Temperature = 21 celsius (room temp)
B = -13.12 x Log10 (Temp + 273) + 34.55 = -13.12 x Log10 (21 + 273) + 34.5 = 2.12
C = Log10 [Ca2+ as CaCO3] - 0.4 = Log10[0] - 0.4 = -Infinity
D = Log10[alkalinity as CaCO3] = Log10[0] = -Infinity
pHs = (9.3 + A + B) - (C + D) = 9.3 + A + B - C - D = 9.3 - Infinity + 2.12 + Infinity + Infinity = Infinity
LSI = pH - pHs = 7 - Infinity = -Infinity
https://www.wolframalpha.com/input?i=7+-+%28%289.3+%2B+%28%2...
From my understanding a negative LSI means the water will try to "pick up" atoms/molecules from the container it is in (corrosive). A positive LSI indicates it will lay down atoms/molecules (scale build-up).
A value of negative infinity tells me that pure water is going to eat the pipes.
That being said, I don't know if the LSI scale is well behaved as these values trend towards 0! The values of water purity in the equation seem to dominate both pH and temperature as those values trend towards 0 - no big difference in results if pH is 7 vs. pH is 3 and no big difference if water is frozen or boiling. Temperature can have a big impact for _very cold_ and _very hot_ but then you're dealing with solid water or steam and that doesn't really make sense to me for this model. That probably suggests the equation is only well behaved for a certain range for each value, and I'd suspect 0 is outside the range these equations can model for TDS, Calcium, and Alkalinity. But I can't find anything that defines the ranges the LSI model applies to.
I wonder what you think the pH of steel wool is. I bet you could place steel in a copper pot and it won’t eat through it.
Your assertion is that 'pure water' will corrode copper pipe, so it needs to be 'impure' to not do so (using flouride of all things as an example?)
Yet, distilled water - which is as pure water as anyone will ever see outside a lab - doesn't do so to any meaningful extent. And you keep using various clearly inapplicable theory to try to prove a point that is clearly false in the real world.
This has nothing to do with steel wool, after all.
I haven’t been able to find a source since posting this. I may have my facts backwards! The closest I have is this CDC report saying it reduces corrosiveness: https://www.cdc.gov/fluoridation/engineering/corrosion.htm
My understanding is that, if you take fluoride out of the water, you’ll need to replace it with something or the water will replace it itself (aka eat the pipe).
That obviously doesn’t mean fluoride was originally added for that reason though.
The only thing I could think of that might have corrosive issues would be desalination water that was overly purified like the sibling comment mentioned. But even then, they should be adding some kind of minerals back before distributing it to people's homes. Ultrapure water tastes horrible and likely isn't safe for drinking long term.
I’m totally open to being wrong. I’m eager to learn - which is generally why I share information. If I don’t readily share what I know to be true, like in this case, nobody will ever correct me and I’ll spend the rest of my life being incorrect.
On HN you generally start by telling someone why they’re wrong and supporting that in some way.
I.E. if you know/believe fluoride was added for another reason - that’s a good place to start.
Or if you know/believe purified water is not corrosive, that would be a good place to start.
We had a city in Illinois do whole city RO and advertise the cleanest water in the country. Well it was the cleanest water going into the pipes, but if you own a house in that city the water coming out of your tap is full of old pipe!