What's in my water
Water hardness — what causes scale, and why RO is usually the wrong fix for it
Total hardness is the combined concentration of dissolved calcium and magnesium, expressed as milligrams per litre of equivalent calcium carbonate, and it is what forms scale on every surface hot water touches.
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 | 200 mg/L as CaCO₃ | — |
| BIS IS 10500:2012 — permissible in absence of alternate source | 600 mg/L as CaCO₃ | — |
| BIS — calcium | 75 mg/L acceptable, 200 mg/L permissible | — |
| BIS — magnesium | 30 mg/L acceptable, 100 mg/L permissible | — |
| WHO | No health-based guideline value | — |
Where it comes from
Limestone and dolomite aquifers
Groundwater moving through carbonate rock dissolves calcium and magnesium. This is the dominant source.
Deccan basalt
Produces moderately hard water across much of Maharashtra, and it is why Pune and Nashik supplies behave the way they do.
Alluvial groundwater
The Indo-Gangetic plain generally produces hard to very hard groundwater.
Long aquifer residence time
Arid regions with low recharge concentrate hardness, which is why Rajasthan and Gujarat groundwater runs high.
Why it matters
- Scale coats heating elements in geysers, washing machines and kettles, raising electricity consumption and shortening appliance life. This is the biggest measurable cost of hard water.
- Soap and shampoo lather poorly and leave a residue, which is the origin of the widespread complaint about hair and skin in hard-water cities.
- White chalky deposits form on taps, tiles and glassware and are difficult to remove permanently.
- There is no established health harm — WHO does not set a value, and some studies have suggested a protective association with cardiovascular outcomes, which is not strong enough to act on either way.
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? | Poor lather, a slippery-then-squeaky feel after washing, white deposits around taps and on the kettle element, and spotting on dried glassware. |
| Does a TDS meter show it? | Hardness contributes to TDS but is not the same thing. Water at 400 ppm TDS could be 350 mg/L hard, or almost entirely sodium chloride with hardness near zero. The meter cannot tell you which, and softener salesmen frequently rely on that. |
| Field / home test | Soap-solution titration kits and hardness test strips are cheap, accurate enough for the decision, and available for ₹200–500. This is one of the few field tests genuinely worth doing yourself. |
| Laboratory test to ask for | Total hardness by EDTA titration — APHA 2340 C, with separate calcium and magnesium by 3500-Ca/Mg (indicative ₹150–₹500) |
When to pay for a laboratory test
- You are quoted for a whole-house softener. Get an independent hardness figure first — softener sizing depends entirely on it, and the seller's number is the seller's number.
- Geyser or washing machine heating elements have failed more than once.
- You want to know whether your problem is hardness or high TDS generally, because the two need different equipment.
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.
- Ion exchange softener (whole-house)Effective
Near-complete removal of calcium and magnesium
The correct technology for a hardness problem. Resin exchanges calcium and magnesium for sodium, and regenerates with salt.
Caveat: Adds sodium in proportion to the hardness removed. On very hard water that is a genuine consideration for anyone on a sodium-restricted diet — soften the bathroom and utility lines, not the drinking tap.
- Reverse osmosis (RO)Effective
Removes hardness along with everything else, at the drinking tap only.
Caveat: Solves nothing about scale, because your geyser and washing machine are not fed from the RO tap. Buying RO to fix hard water is treating 1% of your water volume and hoping.
- Antiscalant dosingPartial
Does not remove hardness but keeps it in solution so it does not deposit as scale. Standard as RO pre-treatment; used in commercial systems.
- Template-assisted crystallisation (TAC / salt-free conditioners)Depends
Converts dissolved hardness into microcrystals that are less prone to adhering to surfaces. Hardness is not removed — soap performance is unchanged.
Caveat: Genuine mechanism with independent test data behind it, unlike magnetic devices, but the benefit is scale prevention only. Do not accept it as a substitute for softening if lather is the complaint.
What does not work
Each of these is commonly assumed — or actively marketed — to help with total hardness. None of them do.
UV
No effect on dissolved minerals of any kind.
Activated carbon
No meaningful capacity for calcium or magnesium.
UF
Pore size is far larger than a dissolved calcium ion.
Magnetic and electromagnetic descalers
Sold widely and on the strength of testimonials. Independent controlled testing has not demonstrated a reliable effect, and there is no accepted mechanism. Do not spend money here.
Boiling
Boiling precipitates temporary (carbonate) hardness as scale — which is exactly the deposit in your kettle. It leaves permanent hardness behind and does not soften the water you drink.
The mistake almost every hard-water household makes
The complaint is scale on the geyser, spots on the glassware, and hair that feels wrong after a shower. The purchase, overwhelmingly, is a drinking-water RO system.
A domestic RO unit treats the water that comes out of one tap in the kitchen. That is somewhere around 1% of household water use. The geyser, the shower, the washing machine, the dishwasher and the taps that produce every symptom on the list are all fed from the untreated line.
So the scale keeps forming, the lather stays poor, and the household concludes that water treatment does not work. It did work — on the wrong 1%.
If your problem is scale and lather, the equipment you want is a whole-house softener on the inlet, and it typically costs less than a premium RO system. If your problem is high TDS and taste at the drinking tap, you want RO. If you have both, you want both, and the softener goes first in the sequence.
Tip
Reading a hardness figure
The classification bands above are the conventional WHO descriptive scale. The BIS acceptable limit of 200 mg/L sits at the top of 'hard', and the permissible fallback of 600 mg/L is a very long way into water that will cause daily practical problems.
| Total hardness (mg/L as CaCO₃) | Classification | What you will notice |
|---|---|---|
| 0–60 | Soft | Excellent lather; can be mildly corrosive to metal fittings |
| 61–120 | Moderately hard | Little scale; no practical complaints |
| 121–180 | Hard | Visible scale on kettles and geysers within months; noticeably more soap needed |
| 181–200 | Hard — at the BIS acceptable limit | Persistent tap and tile deposits; appliance descaling becomes routine |
| Over 200 | Very hard — above BIS acceptable | Rapid scale build-up, poor lather, shortened heating element life |
Frequently asked questions
Is hard water bad for health?
Water softener or RO for hard water?
Does hard water cause hair fall?
Do magnetic water softeners work?
How much does a water softener cost in India?
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.