Magnesium
The other half of hardness. Contributes scale, a slight bitterness, and a laxative effect at high levels.
- Measured in
- mg/L
No range is shown because none is published. Magnesium is a nutrient, and what matters practically is total hardness — see that guide.
What it is
Magnesium dissolves into water from dolomite and magnesium-bearing rock. With calcium it makes up total hardness, and it is usually the smaller of the two.
Why it matters
Like calcium, magnesium is a nutrient rather than a contaminant and has no drinking water limit. It contributes to scale, though it deposits differently from calcium, and at high concentrations it gives water a slightly bitter taste and can have a mild laxative effect — usually alongside sulfate, since magnesium sulfate is Epsom salt. For anyone building water for coffee or tea, the calcium-to-magnesium ratio matters more than the total.
How to measure it
A laboratory panel reports it separately. Home hardness tests fold it in with calcium and cannot separate the two.
Certified laboratory, mail-in kit
- How trustworthy
- Reference grade
- Cost
- Most expensive
- Effort
- Careful sampling, then days or weeks of waiting
You are posted bottles and instructions, you fill them exactly as told, and you post them back. Weeks later a report arrives with figures nobody has to interpret by eye. This is what a result you intend to act on should be built from.
Its own line on a general chemistry panel. Worth having separately if you are building brewing water, where the ratio to calcium is the point.
Where to find it: State-certified drinking water laboratories; your state's certification officer keeps the list, and many public health departments will point you at one.
Test strips
- How trustworthy
- Ballpark
- Cost
- Low cost
- Effort
- Under a minute, wherever you drew the sample
A plastic strip with reagent pads on it. Dip it, hold it level, and match each pad against the chart on the bottle at the time the label tells you to. Most strips read several parameters at once.
A hardness strip includes magnesium in its total and cannot report it alone. Sufficient for scale decisions, not for a recipe.
Where to find it: Pool shops, hardware stores, supermarkets and online, sold both per parameter and as multi-packs. Buy strips made for your kind of water: pool strips and drinking water strips read very different scales for the same chemistry.
Your utility's annual water quality report
- How trustworthy
- Reference grade
- Cost
- Free
- Effort
- A few minutes of reading
Every community water system in the US has to publish one each year, free, listing what it found and what the limits are. It is real laboratory data about the water leaving the plant and travelling the mains. What it cannot describe is your own plumbing.
Published by many systems as part of a mineral analysis.
Where to find it: Your water bill, your supplier's website, or the EPA's index of reports. It is also called a Consumer Confidence Report or CCR.
Further reading: US EPA: Consumer Confidence Reports, the annual report every community water system publishes
If it is too low
Nothing to act on.
- • No action needed.
If it is too high
Contributes to scale and can taste faintly bitter. A laxative effect is possible where magnesium and sulfate are both high.
- • Treat it as hardness: descale, soften, or inhibit scale according to how much trouble it is causing.
- • If there is a laxative effect, look at sulfate as well; the two usually travel together.
Common questions
Can I get my daily magnesium from drinking water?
Water contributes, and in hard-water areas that contribution is not trivial, but food supplies most of it. Softening water removes magnesium along with calcium, which is a small dietary loss rather than a meaningful one.
Why do coffee recipes care about magnesium specifically?
Magnesium and calcium extract flavour compounds differently, and magnesium is generally considered the better extractor. That is why coffee water recipes specify the two separately rather than giving a single hardness figure.
WiseWaterGauge helps you record and understand your own readings. It is not a substitute for a certified laboratory test, and nothing here is medical or regulatory advice. If a health parameter is out of range, confirm it with an accredited lab and speak to your water provider.