The short answer: Porosity is just how open your cuticle scales sit, and hard water pushes them the wrong way. Calcium and magnesium settle onto the shaft and, on already-lifted hair, let more moisture rush in and out, while on tight low-porosity hair they build a calcium-soap scum on the surface. One trigger, two failure modes. A chelating wash that lifts those minerals off at an acidic pH is what stops the next round of damage. deSal Hard Water Defense (pH 5.45, about ₹765) is built for exactly that.
I love this topic because everybody talks about porosity like it is your hair's personality, when it is really just chemistry you can see under a microscope. Let me walk you through the mechanism, and bust the one myth that ruins most home diagnoses.
What hair porosity actually is (cuticle scales, not personality)
Every strand is wrapped in a cuticle, a layer of overlapping keratin scales that lie like tiles on a roof. Porosity is nothing more than how flat or lifted those scales sit.
Flat and tight equals low porosity: moisture and product have a hard time entering, yet once inside they stay put. Raised or eroded equals high porosity: moisture rushes in and escapes just as fast, so the hair frizzes, drinks product, and dries out. Medium sits between, and it is the easiest to live with. And here is the bit people miss: you are almost never one porosity across the whole head. Your ends are older and more weathered than the roots, so they read as higher porosity. That is normal ageing of the fibre, not a diagnosis.
Myth: the float test tells you your porosity
Here is the myth I want to kill. The float test, drop a clean strand in a glass of water, sink equals high porosity, float equals low, is treated as gospel online. It is not a measurement. It is a coin toss wearing a lab coat.
The correct version: whether a strand floats or sinks depends on trapped air, surface oils, product residue, and the sheer weight of the hair as much as on cuticle state. Labs do not use it, and neither should you as a verdict. If you want a home read, a drying-time check (how long a section takes to air-dry) and a slip test (running fingers up the strand and feeling for roughness) both give steadier signals. Use them as hints, not certainty. The only real porosity readout comes from electron microscopy of the cuticle, and your bathroom does not have one.
How hard water raises porosity over time
Now the mechanism, which is well established. Hard water carries dissolved calcium and magnesium, the two ions that define hardness. The two settle onto the shaft, and when they meet shampoo surfactants they throw down an insoluble scum, the very calcium stearate that rings your bucket. That deposit is abrasive and it sits alkaline, and an alkaline surface lifts the cuticle. Repeat that daily for months and healthy medium-porosity hair drifts toward raised, thirsty, high-porosity hair.
There is measured harm behind this, not just theory. In a controlled study, hair soaked in genuinely hard water showed lower breaking strength than the same hair in distilled water, roughly 234 versus 255 (PMC6028999, P=0.001). A separate study at a lower hardness, about 212 ppm, found no significant difference (PMC3927171), which is the honest nuance: the damage scales with how hard your water actually is. And India runs hard in a lot of places. The Central Ground Water Board maps groundwater hardness across aquifers, and the WHO bands put anything above 180 mg/L as CaCO3 in the "very hard" range, which a great many Indian metros clear comfortably.
High porosity or low: where does hard water do more harm?
Both suffer, in opposite directions, which is why the fix differs. Where porosity is already high, the cuticle sits open, letting calcium travel to the cortex faster and speeding up erosion, dryness and breakage. Where porosity is low, the sealed cuticle blocks penetration but gathers that stubborn calcium-soap scum on its outer face, so the strand feels coated, heavy and resistant to product. Same trigger, two failure modes: erosion on the high side, build-up on the low side. High porosity wants sealing and a protein-moisture balance; low porosity wants lightweight products and regular removal of the mineral coat.
What actually protects the cuticle
Two levers do the heavy lifting: get the mineral load off the hair, and keep the wash acidic so the cuticle lies flat. An acidic pH matters more than people think. A survey of over a hundred shampoos found most run too alkaline (PMC4158629), and alkaline washing raises cuticle friction, which is exactly the roughness and breakage you are trying to avoid. Match the hair's own 4.5 to 5.5 range and the scales settle instead of standing up.
This is the job a chelating shampoo is built for. Chelators like Disodium EDTA grab and hold the calcium and magnesium bound to the fibre and let you rinse them away, rather than leaving them to build wash after wash. A quick word on the popular alternatives, without pretending they are the same job. A shower filter is genuinely good at chlorine and sediment, but it does not remove the calcium and magnesium hardness. Measure the TDS before and after one and it reads about the same, which means the hardness still reaches your hair. A filter that claims to "condition" or "sequester" minerals is doing something to the water, not lifting off what is already bound to the strand. And a treatment that neutralises a metal but leaves it parked inside the fibre is a weaker move than lifting the mineral off and rinsing it out. A plain clarifying shampoo strips oil and product, but it may not chelate metal ions at all.
Where deSal fits
deSal Hard Water Defense is a chelating shampoo built for this exact problem: Disodium EDTA plus citric acid at pH 5.45, with panthenol, hyaluronic acid and argan oil to put moisture back in the same wash so the cuticle does not read "stripped". 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, bench-tested against genuinely hard water above 500 TDS rather than clean lab tap, which is the part that actually takes effort. It is in-vivo tested for skin safety (Mascot Spincontrol: dermatologically tested, clinically tested, non-irritant). The chelation is established chemistry that removes bound calcium and magnesium.
FAQ
Can high-porosity hair be reversed? Not really. After scales have lifted or worn away, there is no permanent rebuilding of that damage, so the play is to halt fresh harm and grow the affected length out. Fresh growth arrives in better shape once your water and washing routine improve.
Does hard water lead to high or low porosity? It drives each one, but along opposite paths. Where hair is already porous, calcium keeps wearing the cuticle down and porosity climbs. Where the cuticle stays shut, those same minerals leave a soap scum sitting on top. Two kinds of damage from a single hard-water cause.
How do I test my hair porosity at home? At best the float test offers a loose hint, and oils, residue and the weight of the strand throw it off easily, so never read it as a verdict. Timing how long a section takes to dry, or a slip test, holds up better. A true porosity reading only comes from microscopy, not from a glass of water.
Is a chelating shampoo the same as a clarifying shampoo? Not quite. Clarifying strips oil and product buildup; chelating specifically binds metal ions like calcium and magnesium. Many chelating shampoos clarify too, but a plain clarifying shampoo may not chelate.
Sources
- Hard water, calcium deposition and reduced hair breaking force (~234 vs ~255, P=0.001): PMC6028999
- Lower hardness (~212 ppm) showed no significant difference in breaking strength: PMC3927171
- Shampoo pH, most formulas too alkaline, acidic pH cuts cuticle friction: Gavazzoni Dias et al., Int J Trichology 2014, PMC4158629
- WHO drinking-water hardness bands (soft, moderately hard, hard, very hard as mg/L CaCO3): World Health Organization
- Indian groundwater hardness mapping across aquifers: Central Ground Water Board (CGWB)
