Alkalinity

Summary: Alkalinity is your water’s buffering capacity—its ability to resist pH change. It mainly comes from bicarbonate (HCO₃⁻) and carbonate (CO₃²⁻) ions and is reported as mg/L (ppm) as CaCO₃. Low alkalinity lets pH swing (corrosion risk). High alkalinity stabilizes pH but can promote scale with hardness.

Why homeowners should care

Alkalinity, together with pH and hardness, drives whether your plumbing tends to corrode or scale. Stable, moderate alkalinity helps keep metals like copper and lead from dissolving and reduces nuisance scale in heaters and fixtures.

What alkalinity really measures

Units: mg/L (ppm) as CaCO₃.
What it is: Mostly bicarbonate/carbonate; small contributions from hydroxide/borate/phosphate when present.
How it behaves: Higher alkalinity buffers pH (more stable). Lower alkalinity = pH bounces with aeration, CO₂ loss, or treatment changes.

When to test

At move-in or when starting a private-well baseline.
Annually for private wells; seasonally if water chemistry swings with wet/dry periods.
Whenever you see corrosion signs (blue-green stains, pinhole leaks) or persistent scale.
Before/after installing neutralizers, softeners, or RO to verify effect.

How we test

HealthWaterLab measures alkalinity by laboratory titration/photometric methods and can pair results with pH, hardness, calcium, conductivity/TDS, and metals (lead/copper) to interpret corrosion/scale tendencies.

How to collect a good sample

Use the kitchen cold-water tap (or raw water upstream of treatment if we’re sizing equipment).
Run water several minutes to bring in fresh water (unless first-draw is requested for metals workups).
Fill to the marked line; cap immediately; deliver promptly—exposure to air can shift CO₂ and slightly change alkalinity/pH.

How to read your result (homeowner version)

< 40 mg/L (low): Poor buffering; pH may swing and corrosion risk rises—evaluate copper/lead and consider raising alkalinity.
40–120 mg/L (moderate): Good general range for most homes; balance with hardness to limit scale.
120–240 mg/L (high): Stable pH but more scale with hardness, especially in hot water; manage scale or consider blending/treatment.
> 240 mg/L (very high): Expect strong scaling tendency; plan scale control and consider point-of-use RO for taste/appliances.

Practical ways to manage alkalinity

Raise low alkalinity: Acid-neutralizing calcite filters or soda-ash injection. Re-test because neutralizers also raise hardness (you may add a softener).
Lower very high alkalinity (for scaling/taste): Point-of-use RO at the kitchen tap lowers alkalinity/TDS where you drink/cook. Whole-home reduction typically requires blending or chemical feed under professional guidance.
Stabilize pH: Aim for adequate alkalinity plus a pH around 7–8 for most homes; avoid long stagnation and keep well caps/seals tight.
Verify: After any change, re-test alkalinity with pH/hardness and check metals if corrosion was a concern.

FAQ

How is alkalinity different from pH?

pH is the instant acidity/basicity. Alkalinity is the buffer that resists pH change. You can have a neutral pH with very low alkalinity that swings easily.

Does a softener change alkalinity?

Not much. Softeners swap calcium/magnesium for sodium/potassium but leave alkalinity similar. They reduce scale even when alkalinity stays the same.

Will reverse osmosis (RO) lower alkalinity?

Yes—RO at the kitchen tap removes many dissolved ions, including bicarbonate/carbonate, lowering alkalinity and TDS for better taste and less kettle/coffee scale.

Why does my pH “bounce” after aeration or storage?

Low alkalinity water can change pH when CO₂ is added/removed (aeration, standing). Raising alkalinity increases buffering and stabilizes pH.

Can I use baking soda to raise alkalinity?

It will raise alkalinity temporarily, but dosing is tricky for whole-home plumbing. For a permanent, consistent fix, use calcite/soda-ash systems sized for your flow.

Does high alkalinity always mean more scale?

High alkalinity with hardness and heat promotes scale. Manage by softening, lowering heater temperature, periodic descaling, or using RO at the drinking tap.

Will raising alkalinity reduce lead/copper?

Often, yes—adequate buffering with suitable pH can reduce metal leaching. If you have older plumbing or lead service materials, test lead/copper to confirm.

Pool test strips say my alkalinity is “fine.” Is that valid for drinking water?

Pool ranges are for disinfection control in pools, not household plumbing. Use lab results and home-plumbing guidance for drinking water decisions.

Does boiling change alkalinity?

Boiling can precipitate some carbonate scale, slightly lowering alkalinity in the pot—but it concentrates the remaining minerals. It’s not a treatment strategy.

Why do I still get scale after raising low pH with calcite?

Calcite adds calcium and alkalinity, which can increase scale potential. Pair with a softener or use RO at the kettle/coffee tap to protect appliances.

How often should I retest alkalinity?

Annually for private wells; after installing/servicing neutralizers, softeners, or RO; and whenever corrosion/scale/taste changes appear.

Want a stable, balanced water chemistry? Order alkalinity testing (with pH/hardness pairing) and get step-by-step guidance at HealthWaterLab.com.