The symptoms are your plumbing dissolving
| What you see | What it is |
|---|---|
| Bluish-green stains in sinks and tubs | Copper corrosion |
| Metallic taste, worst in the first water each morning | Copper |
| Small pinhole leaks in pipework | General corrosion |
The morning detail matters. Water that has stood in the pipes overnight has had the longest contact time, so it carries the most dissolved metal. A sample drawn mid-day, after the household has been running taps, can come back clean from a system that is actively corroding.
What actually makes water corrosive
Penn State Extension’s water team notes that “water that is soft and acidic (pH < 7.0) tends to be more corrosive.” EPA’s secondary range for pH is 6.5 to 8.5, and below it EPA lists corrosion as a noticeable effect.
But pH alone is not the measure. The standard is the Langelier Saturation Index, which combines pH with hardness, alkalinity and temperature: “Negative values of the LSI indicate corrosive water while positive results indicate non-corrosive water,” and the target is an LSI greater than zero.
Soft and acidic is worse than acidic alone — which is why well owners with naturally soft water see corrosion at pH values that cause no trouble elsewhere.
Why this is a health issue and not a cosmetic one
The acidity is not what harms you. What it dissolves is.
Lead is the serious one. The primary drinking water standard is 15 micrograms per litre, or 15 parts per billion. Long-term exposure is associated with cancer, stroke and high blood pressure in adults, and with premature birth, reduced birth weight, seizures, behavioural disorders, brain damage and lowered IQ in children.
Lead does not usually come from the aquifer. It comes from solder, fittings and fixtures — and corrosive water is the mechanism that moves it into your glass.
Copper has a primary standard of 1.3 mg/L for severe stomach cramps and a secondary standard of 1.0 mg/L for taste and staining.
Two ways to correct it, and they are not equivalent
Neutralising filter
A tank of alkaline media — “calcium carbonate (limestone) chips, marble chips, magnesium oxide, or other alkaline material” — that raises pH and adds calcium as water passes through.
It also raises hardness. Penn State Extension states this outright: “this process will increase the hardness of the water, but this is necessary for proper corrosion control.”
That is the sentence that changes your build order.
Soda ash injection
A chemical feed pump dosing soda ash or sodium hydroxide, installed “before the pressure tank.” Penn State notes “soda ash is preferred over sodium hydroxide because it is safer to handle.”
Injection raises pH without adding hardness. That is the reason to choose it despite the added complexity of a pump and a solution tank.
Mistakes that cost the most money
Sizing the softener on the raw test. A neutralising filter adds calcium, so hardness after treatment is higher than the number you started with.
Treating pH last. Acidic water attacks copper plumbing and degrades every component installed downstream, including equipment not yet bought.
Reading blue-green staining as a dye problem. It is copper coming out of your own pipes, which means the plumbing is the thing being consumed.
Choosing soda ash without accounting for the pump. Injection needs a feed pump and a solution tank kept topped up. It is lower maintenance than corroded plumbing, but it is not zero.
Three situations, and what changes
Low pH, no equipment yet. A neutralising filter is simplest, provided the softener that follows is sized on hardness measured afterwards.
Low pH, softener already installed and sized. Soda ash injection raises pH without adding hardness, so the existing sizing stays valid.
Low pH plus high hardness already. Injection again, because a neutraliser would push hardness further up and enlarge the softener you need.
The objections worth answering
“The water tastes fine.” Corrosion is a plumbing and metals problem, not a taste one. EPA lists corrosion as the noticeable effect below pH 6.5, and the evidence shows up on fixtures first.
“Can I just replace the pipes?” That addresses the damage, not the cause. The replacement plumbing meets the same water.
“Is a neutralising filter maintenance-free?” No. The media dissolves by design, so it is consumed and must be topped up. That is the mechanism working.
Who this is for
Private-well households with a pH result below 6.5, or blue-green staining, deciding between neutralising media and chemical injection.
Choose a neutralising filter if
- Your pH is below 6.5 and no softener is installed yet, or you are buying both.
- You would rather not run a chemical feed pump and a solution tank.
- You can size the softener on hardness measured after the neutraliser.
Choose soda ash injection if
- Your hardness is already high and you do not want calcium added to it.
- A softener is already installed and sized on your current hardness figure.
- You can manage a feed pump and keep a solution tank topped up. Penn State prefers soda ash to sodium hydroxide because it is safer to handle.
The sequencing consequence most pages miss
If you install a neutralising filter and then a softener, the softener must be sized on the hardness after neutralising — not on your original well test.
The neutraliser has been adding calcium the whole time. Size on the raw figure and you will undersize the softener, which means it regenerates more often, burns more salt, and wears out sooner than its rating suggests.
This is also why pH correction is stage one in the treatment sequence: it changes the water that every later stage has to handle.
→ The same corrosion chemistry, and lead → Blue-green staining, read as a corrosion finding → The full sequence and arithmetic → Softener sizing