The short answer: Put simply, hard water is tap water carrying a lot of dissolved calcium and magnesium, picked up as rainwater seeps through limestone and basalt. Those two ions are over 95 percent of the hardness, and once dissolved they react with soap, keratin, and heat. In India the BIS acceptable limit for drinking hardness is 200 mg/L as CaCO3. A chelating shampoo like deSal binds that calcium and magnesium off the hair and rinses it away.
I read ingredient lists for fun, so let me do the thing I actually enjoy: explain what "hard" means in chemistry, not in marketing. No scare stats, just the mechanism and the numbers your own water report already uses.
What hard water actually is: two ions doing all the work
Hardness is not vague "impurity". It is a measurement of dissolved divalent metal ions, and in Indian supply that means calcium (Ca2+) and magnesium (Mg2+). They account for the large majority of total hardness. Everything else you associate with hard water traces back to these two.
Here is why they matter so much. Both ions are divalent, meaning they carry a double positive charge, and that charge is what makes them so reactive. They grab onto soap molecules and form an insoluble curd, the scum ring in your bucket. They latch onto negatively charged sites on keratin, which is how a mineral film builds up on the hair shaft wash after wash. Clear water tells you nothing, by the way. Calcium and magnesium are invisible at every concentration found in an Indian tap.
How water turns hard: a short geology detour
Rain starts soft, close to pure. On the way down it absorbs carbon dioxide from the air, turning into a mildly acidic carbonic solution. That gentle acidity is the tool. As the water percolates through soil and rock on its way to an aquifer or borewell, it slowly dissolves calcium carbonate and magnesium carbonate out of limestone, dolomite, and gypsum.
Contact time is everything. Deep borewell water has sat against mineral rock for far longer than a fast-moving surface river, which is why groundwater in hard-rock regions runs so much harder than a Himalayan-fed supply. Roughly two-thirds of India sits on granite and basalt geology, so borewell-dependent cities on the Deccan plateau routinely deliver genuinely hard water. Falling water tables push those borewells deeper into more mineralised layers, and Central Ground Water Board (CGWB) data for many Indian cities shows hardness sitting well past the drinking limit.
How hardness is measured, and the myth about TDS
In India, hardness is quoted in milligrams of calcium carbonate equivalent per litre (mg/L as CaCO3), a figure numerically identical to parts per million (ppm). Imported filter packaging often uses grains per gallon instead, where 1 GPG equals 17.1 mg/L, so a device rated for "10 GPG" only covers about 171 mg/L, which barely touches what many borewells here push out.
Now the myth, because there is always one. Myth: a low reading on your pen-style TDS meter means your water is soft. The correct version: TDS is total dissolved solids, and it counts sodium, potassium, chlorides, and sulphates alongside calcium and magnesium. Water can read moderate on a TDS meter while the calcium and magnesium, the exact fraction that scums your shampoo and films your hair, sit high. High TDS usually tracks with high hardness, but they are not the same measurement, and only a proper hardness test tells you the part that matters for washing.
Why the number matters once it hits your hair
This is where I flag the gap between the beaker and the shower. In the beaker, chelation is settled chemistry: a chelator like Disodium EDTA has a well-known affinity for Ca2+ and Mg2+ and locks onto them. On the head, the useful question is what hardness does to a real fibre. In one controlled study, hair soaked in hard water showed a lower breaking strength than hair in distilled water, around 234 versus 255 (PMC6028999, P=0.001). A separate study at a lower hardness near 212 ppm found no significant difference (PMC3927171), which is the honest nuance: concentration matters, and the damage shows up at the high end, as breakage and dryness rather than the shedding people fear.
India's water standards: BIS and the WHO bands
India's drinking-water standard, IS 10500:2012, sets two hardness figures. The acceptable limit is 200 mg/L as CaCO3, the recommended ceiling. The permissible limit, meant only for places with no softer alternative, is 600 mg/L. That upper number is a worst-case ceiling, not a target, and plenty of hard-water cities test between 300 and 600.
For a feel of the scale, the WHO hardness bands read: soft is 0 to 60 mg/L, moderately hard is 61 to 120, hard runs from 121 to 180, and anything beyond 180 is classed very hard. Most Indian borewell supply lands firmly in very hard territory, several times the soft threshold. On drinking safety, WHO notes no convincing evidence that hardness harms health, so this is a contact problem for your skin and hair, not a toxicity one.
Worth a quick note on the popular fixes, since they get sold as the same thing. A shower filter mainly cuts chlorine and sediment, both worth having, but test the water before and after one and the hardness reads about the same, because it does not pull dissolved calcium and magnesium out. That hardness still reaches your hair. A device that claims to "condition" or "sequester" minerals leaves them in the flow rather than off the strand, and a treatment that neutralises a metal and parks it inside the fibre is doing less than lifting it off and rinsing it clear.
Where deSal fits
deSal Hard Water Defense is a chelating shampoo built for exactly the water described above: Disodium EDTA and citric acid at pH 5.45, with panthenol, hyaluronic acid, and argan oil to put moisture back in the same wash. It is about ₹765 for 220 ml, roughly ₹3.5 per ml. It came out of months of formulation work by two IIT Roorkee engineers, and it was bench-tested against genuinely hard water above 500 TDS rather than clean lab tap, which is the part that takes real effort. It is in-vivo tested for skin safety (Mascot Spincontrol: dermatologically tested, clinically tested, non-irritant). The chelation itself is established chemistry that binds and removes the calcium and magnesium stuck to the hair.
FAQ
Is hard water the same thing as TDS? No, they are different measurements. TDS totals every dissolved solid, sodium and chlorides included, whereas hardness tracks only calcium and magnesium, given in mg/L of CaCO3. Water can read moderate on TDS yet low on hardness when the bulk of those solids are sodium salts, so only a dedicated hardness test reveals the part that matters for washing.
What counts as hard water in India? By the WHO bands, hard is 121 to 180 mg/L and very hard is above 180. India's BIS acceptable drinking limit is 200 mg/L as CaCO3, with 600 as the permissible worst-case ceiling. Most borewell supply on hard-rock geology sits in the very hard range.
Can I make hard water soft by boiling it? Only partly. Boiling drives temporary hardness, the bicarbonates, out as scale, but it leaves permanent hardness from sulphates and chlorides untouched, and most Indian borewell water carries that too, so boiled water still leaves residue.
Does hard water cause hair fall? The evidence points to breakage and dryness, not shedding. A study found reduced hair breaking strength at high hardness (PMC6028999), while a lower-hardness study found no significant change (PMC3927171). Hard water weakens and dulls the fibre; treating shedding is a separate, medical conversation.
Sources
- Hard water and reduced hair breaking strength at high hardness: PMC6028999
- Lower-hardness (~212 ppm) study, no significant difference in tensile strength: PMC3927171
- Shampoo pH and cuticle friction: Gavazzoni Dias et al., Int J Trichology 2014, PMC4158629
- Indian drinking-water standard IS 10500:2012 (BIS), hardness limits 200 and 600 mg/L as CaCO3
- WHO hardness classification bands and health-effects note
- Central Ground Water Board (CGWB) groundwater quality data for Indian cities
