Science: hard water in India and worldwide

SCIENCE · Hair basics and keratin · Scalp, sulfates and what damages hair · Hard water · Hair and scalp pH

2b · Hard water in India and worldwide: what the numbers say about Indian water

Water hardness is the amount of dissolved calcium and magnesium, reported as mg/L (the same as ppm) of calcium carbonate. The WHO does not set a health-based limit for hardness. It notes that hardness above about 200 mg/L can cause scale deposition, especially when water is heated. India's standard, IS 10500, sets 200 mg/L as the acceptable limit and 600 mg/L as the permissible limit where no better source exists.

CITY	WHAT PUBLISHED SOURCES SHOW	SOURCE
Bengaluru	A 2018 survey found that 24% of households on a mix of borewell and Cauvery water had hardness above 200 mg/L. About 45% of the city depends on borewell water.^{8, 9}	News: Citizen Matters, Deccan Herald
Chennai	Groundwater sampled in 2012 averaged about 322 mg/L total hardness before the monsoon and 299 mg/L after. Both are above the 200 mg/L acceptable limit.	Peer-reviewed study
Noida and Uttar Pradesh	Across 290 groundwater monitoring sites in 69 Uttar Pradesh districts, about 24% of samples were above the maximum permissible total hardness. A Greater Noida study rated groundwater quality very poor in parts and said it needs treatment before drinking.^{10, 11}	Peer-reviewed studies

Not just India

Hard water is a concern in many countries. Germany is one example: by law, tap water is classed as soft (below 1.5 mmol/L calcium carbonate), medium (1.5 to 2.5) or hard (above 2.5 mmol/L, about 250 mg/L), and suppliers must tell customers their range at least once a year.¹² One third-party compilation of 4,140 locations gives an average of about 15 °dH (roughly 270 mg/L), with harder water in the south and east.

How hair takes up hardness metals: a laboratory study

Researchers at the University of Cincinnati, with a co-author from a hair-care manufacturer, washed virgin and bleached hair swatches in soft, moderately hard and very hard water and measured calcium and magnesium in the hair.¹³ They also tested water at pH 7, 8 and 9. The study used swatches and artificial hardness solutions, not iluvia products.

FINDING	WHAT THE STUDY REPORTED
Hair condition drives uptake	Uptake was very strongly linked to hair condition (r² of 0.98 for calcium and 0.99 for magnesium) and less strongly to water hardness (0.59 and 0.72). Bleached hair held far more of both metals than virgin hair.
Hair has a limit	Hair has a finite number of binding sites. Uptake from water of 9 and 16 grains per gallon (about 154 and 274 mg/L as calcium carbonate) did not differ significantly for virgin and highly damaged hair, and differed by only 16% for slightly damaged hair.
Soft water still counts	Even with repeated washing in soft water (2 grains per gallon, about 34 mg/L), damaged hair took up large amounts. The authors conclude that uptake is not confined to people in hard-water regions.
Calcium over magnesium	Treated hair held seven to nine times more calcium than magnesium, even though the water held calcium and magnesium at 3 to 1.
pH matters	Uptake rose as the water pH went from 7 to 8 to 9, because more binding groups on the protein become available as the pH rises. Hair washed in alkaline water therefore holds more of these metals, and treated hair more still.
Why treated hair binds more	Alkaline peroxide bleach cleaves bonds inside the hair and strips the fatty acid 18-MEA from its surface. This exposes negatively charged carboxylate and sulfonate groups, which make hair behave like a cation-exchange resin. Levels in highly damaged swatches were comparable to those in people who regularly use oxidative colour.

What this means: the hardness of your water is only part of the picture. Colour, bleach and relaxing leave hair able to hold on to far more calcium and magnesium, so mineral build-up can matter wherever the water is hard, moderately hard or even soft.

References

8. Is your water safe to consume? Here's how Bengaluru residents can check water quality. Citizen Matters. citizenmatters.in
9. Almost half of Bengaluru depends on borewell water. Deccan Herald. deccanherald.com
10. Characterization of groundwater potability and irrigation potential in Uttar Pradesh, India using water quality index and multivariate statistics. J Hydroinformatics. 2024. doaj.org
11. Singh S, Hussain A. Water quality index development for groundwater quality assessment of Greater Noida sub-basin, Uttar Pradesh, India. Cogent Eng. 2016;3(1). doi:10.1080/23311916.2016.1177155
12. Gesetz über die Umweltverträglichkeit von Wasch- und Reinigungsmitteln (WRMG), § 9: Angabe der Wasserhärtebereiche. gesetze-im-internet.de
13. Evans AO, Marsh JM, Wickett RR. The uptake of water hardness metals by human hair. J Cosmet Sci. 2011;62(4):383–391.