What's in my water
Magnesium in water — the other half of hardness, and the bitter taste
Magnesium is the second component of water hardness after calcium, and the mineral most often responsible for a distinctly bitter taste in high-TDS groundwater.
Limits and standards
BIS publishes two figures for many parameters: an acceptable limit, and a permissible limit that applies only where no alternate source of water exists. The second is a fallback for communities without a choice — not a target to design a purchase around.
| Standard | Limit | What it means |
|---|---|---|
| BIS IS 10500:2012 — acceptable limit | 30 mg/L | — |
| BIS IS 10500:2012 — permissible in absence of alternate source | 100 mg/L | — |
| WHO | No health-based guideline value | WHO addresses magnesium under hardness and in its assessment of nutrients in drinking water. |
Where it comes from
Dolomite and magnesium-bearing rock
The dominant natural source in groundwater.
Seawater intrusion
Seawater is rich in magnesium, so coastal groundwater affected by intrusion carries it alongside sodium and chloride.
Evaporite deposits
Arid-region groundwater in Rajasthan and Gujarat can carry high magnesium sulphate from evaporite formations.
Why it matters
- Bitter taste is the most common practical complaint, and it appears at lower concentrations than calcium's chalky character.
- High magnesium sulphate concentrations have a documented laxative effect, which is why unfamiliar high-TDS water sometimes causes digestive upset in visitors while residents are unaffected.
- It contributes to total hardness and therefore to scale and soap consumption.
- There is no health-based limit — WHO treats it as a nutrient and hardness component rather than a contaminant.
Note
Can you detect it yourself?
This is the section most purifier buying decisions skip. A handheld TDS meter is the instrument almost every Indian household is shown, and for most contaminants that matter it reads exactly the same whether the contaminant is present or not.
| Question | Answer |
|---|---|
| Can you sense it? | A distinct bitterness, noticeably different from the salty taste of high chloride. If your water is bitter rather than salty, magnesium and sulphate are the first things to check. |
| Does a TDS meter show it? | Contributes to the reading, indistinguishably from anything else. |
| Field / home test | Hardness strips measure calcium plus magnesium together. Splitting the two requires a laboratory. |
| Laboratory test to ask for | Magnesium by EDTA titration or ICP-OES — APHA 3500-Mg B or 3120 B (indicative ₹150–₹500) |
When to pay for a laboratory test
- Water tastes bitter and you want to know whether it is magnesium, sulphate or both — the answer changes whether RO is warranted.
- Visitors report digestive upset from your water while the household is unaffected. Ask for magnesium and sulphate together.
What removes it
Effectiveness ratings below describe the technology working correctly, within its service life, on water or air that suits it. “Depends” means there is a condition in the caveat that decides the outcome — read it before buying.
- Reverse osmosis (RO)Effective
95–98%
Magnesium is a doubly-charged ion and is rejected very efficiently — better than sodium or nitrate.
- Ion exchange softenerEffective
Removes magnesium along with calcium, exchanging both for sodium.
- DistillationEffective
Complete removal; impractical at household scale.
What does not work
Each of these is commonly assumed — or actively marketed — to help with magnesium. None of them do.
UV, UF, carbon and sediment filtration
None remove dissolved magnesium.
Boiling
Concentrates it. Some magnesium precipitates as scale, but the water you drink is not softened.
Frequently asked questions
Why does my borewell water taste bitter?
Does RO remove magnesium?
Is magnesium in water good for you?
Sources
Every limit and standard quoted on this page comes from one of the documents below. Where a figure is not in one of these, we have not published it.
Bureau of Indian Standards · published 2012-05-01 · checked 2026-08-01
BIS states two figures for many parameters: an 'acceptable limit' and a 'permissible limit in the absence of an alternate source'. The second is a fallback for communities with no other supply, not a target.
Guidelines for Drinking-water Quality, 4th edition incorporating the 1st addendum
World Health Organization · published 2017-04-01 · checked 2026-08-01
This page states what published standards say and what the physics of each technology allows. It does not state what is in your supply — no page can. Where the two questions meet is a test result, and every entry in this library says which test to ask for.